Best build / area(s) / difficulty for gem farming?

I DO NOT TAKE ANY RESPONSIBILITY - especially for builds tested on a single player, with perfect items (Nightmare: Dudu and Auradin) - can not tell if multi has or has not something set differently.

tl;dr ? - there is "summary" as the last part of post (Ctrl + F for search).

If You are only aiming for gems, then normal / nightmare difficulties are best, because You can take mobs with one hit there.

Anyway, cow level is the best, as its easy to get there, has a lot of mobs, only uniques can have immunities, there are no doors to open... .
Other than this: Act2 Halls of the Dead, Viper Temple, Tal'rasha Tomb .. but, there are doors.. so teleport is advised and after one TP's out from there, will need to walk thru half of Luth Golein for WP.

I have never tried auradin..., but ...

.. it should work pretty well.

For normal also java (titans and as much faster run/walk items as You can get ;P) and nova soso (faster than java!) - even dirt cheap (just kill nightmare travi a few times for viper, peasants crown, lidless and make a spirit sword (shaco, and spirit shield would help with mana pool and occulus with its Vigor aura, so You would run to Akara/WP portal faster). Aim for enough damage from nova, so that ordinary cows would fall in one shot.

For nightmare:
- java with: random Titans, valkyrie wing helm, razor tail belt, cats eye amu, 30-40 FRW boots, mana leech ring, could add a shield/armor with random light RBFs;
- nova soso (would need crescent moon/oculus with rbf, shaco with rbf [or better griff..] torch, anni, some skillers to be able to one-shot cows here - highest rune here is Vex... if I remember right, personally I got a couple of Ists while farming gems at start. );

PS. Don't bother with killing high resistance cows, just move to another group (unless You want that Cow King set really bad).

UPDATE - Nova soso

I tried a Nova soso on nightmare cows:
- Griffon RBF,
- viper RBF,
- Occu RBF,
- 2x 10 fcr rings.. - I was aiming for 200 FCR (but got stuck at 190 - I need a better amulet - i dont wanna to use hoto here), but even with 2x SOJ, she would still be lacking quite much
- arach
- spirit
a few Light skillers (4.. or 5) - I wanted to keep as much inventory space as possible for charms, jewels and gems.

Nova max damage was slightly above 2k, she needed two hits to kill a Hell Bowine, but when I focused a bit on timing swithing nova-teleport skills well, she was faster than not-best-geared and lously played Javazon (random titans, valkyries wing helm+ias, monarch+4 random rbfs viper+ias, gloves 20/1), but lost hard when Java used perf griff+ias, 4 rbf armor, same shield, 20/2 gloves.
It would help greately if Nova could be used on left skill slot.

I have not tried:
- Ormus,
- Crescent Moon in 1 handed weapon (Shael Um Tir / -35% enemy light res),
- Eshuta's,
- wearing Infinity on soso (conviction woulnt be best here - since we want to kill Cows before it would have a time to get applied, so only impostant stat is -45%-55% enemy light res.).

Other than Eshuta 3/20 or Ormus 15/Nova I don't think it would help much (or at all, since to use Infinity she would lose 5 skills and +5/-5 rbf, so its quite possible that damage would fall)
From what I saw, at this point, adding each skiller adds about 100 damage to Nova (with growing rates - because of +% bonuses), I have place for another 16 skillers .. so maaybe it would be possible to reach 4k nova max damage, but then collecting all the gems, jewels and charms would become really annoying


UPDATE - Auradin

PPS. I just made an auradin. Clearing cows on normal, without picking anything from the ground, took 58 seconds (on the first try - without killing cow king - it takes 3 aura ticks, or a Charge to take him down).
And it is the fastest from all characters I have checked untill now (Nova, Java, Ele dudu).
Nova soso can... finish whole run (town-tristram-clearing cow level) faster but will need ~105+ FCR (I have not tested 200 FCR one), good ping, auto tele, and a good timing from You (for switching Teleport - Nova at the right moment - shame that Nova can not be used under "left" skill tab - it would make it easier).
Auradin is easy.. and very fast.

I am using holy fire aura (possibly holy freeze would be better - in terms of damage, as it seems to be higher, but I have not tested it).
I moved around with Charge skill, while Hole Fire aura was constantly active.

Skills:
Holy fire 20,
Salvation 20 (bonus),
Fire resistance 20 (bonus),
Vigor 1,
Charge 1.

Items:
Head: +2 skills (I use Shaco, but could use some circlet +2 pala / +3 offensive),
Weapon: unique Scepter +3 pala skills with +5% fire RBF - I was missing a few points in damage (could shop for a scepter +pala skills / offensive / holy fire, or use Spirit (and get extra point somewhere else),
Shield: Spiked shield+3 pala offensive (shopped from Anya, hell),
Amulet: +2 skills,
Rings: 2x bul kathos ring,
Charms: 3 offensive skillers
Armor: Trang oul (40 FRW)
Boots: Natalia (40 FRW)
Belt: will be Mavina (20 FRW)

Stats:
Str - enuf for gear
Dex - enuf for gear
Vit - none
Ene - everythig else (Charge takes 9 mana per use)

To tell You the truth... I dont know if there is any use for that extra FWR (other than moving in town) since Charge has fixed movement speed.
Could use +skills armor instead - viper / spirit shroud / skullders.. or Principle +2 pala skills (Ral Gul Eld), socket helm and shield (with possibly 2 sockets each) and place some random fire/cold RBFs and not use skillers / bul kathos rings. - In case someone though, that its hard for a newbie to get those.

My Noobdin's Holy Fire deals 353,7-365,3 aoe fire dmg.
Normal difficulty's cows (non-elite) have up to 342 HP.. sometimes they disappear before I even can hear their "Mooo".

Like I mentioned before, Holy Freeze could end up being easier in reaching 342+ minimum damage, making it even better for completely new players.

UPDATE Nr2 - Holy Freeze

I resetted stats and skills at Akaras shop, added 20 to Holy Freeze, Salvation, Cold Resistance, kept the same items (even Fire RBF), cold aura damage range is: 550-556.
I'll try with 15% Ormus+ RBF, Nighwings Veil (random) + RBF, .. and i will try to find a scepter +3 holy freeze+ 5 sockets.. (for now 3 pala 2 socks).

IMO a build with Dream helm, shield, Dragon armor, Hand of Justice weapon + conviction is not that good, because conviction has lower range and it does not get applied instantly (it takes about 1-1,5 second), in that time, when Auradin would need to wait for it to work, Java would already have a group of cows ripped to shreds and be on her way to another. Because of that I will not bother to try it out.

UPDATE Nr3 - Holy Freeze
I have tried it on a single player:

20 Holy Freeze
20 Salvation
20 Cold Resistance
Helm: Nightwing Veil (RBF) +2 all skills, +20% cold, -5% cold,
Body: Ormus (Rbf): +20% cold, -5% cold,
Belt: Arach +1 all skills
Rings: 2x Soj +2 all skills
Shield: +3 Auras +/- 10% cold (2 sockets with RBFs it's impossible to get better one.. as long as a know)
Weapon: Scepter +3 auras +/-25% cold (5 sockets) / other option would be +3 auras + 3 holy freeze +2 sox, which I have not tried.. but..

Whith those, and 15 Skillers..., it was still far from enough to one-shot Nightmare Hell Bovines. Max damage form cold aura was below 2k.
I think its safe to say, that Java is the best choice for nightmare cows.

Updade Nr4 - Hurricane Dudu

Tried it on single player.
Helm: Nightwings Veil with RBF
Helm2: Magic Pelt +3 ele, +3 Hurricane, +2 RBFs,
Weapon: Flail with 5 RBFs
Weapon2: HOTO
Shield: Monarch with 4 RBFs
Shield2: Spirit
Armor: Ormus with RBF
Armor2: Templar with RBF
Belt: Arach: +1 skills
Rings: 2x SOJ: +2 sills (or one 10FCR ring)
Skillers: .. from 3 to full inventory (ended up with 11 - read below)

Build with Pelt, Ormus, RBF Flail and Monarch is doing higest damage, needed only 3 skillers in inventory... but had to run around.., which with Hurrcanes short range (similar to Nova), was not very effective (Nova soso was faster).

When Armor was switched for Templar's Might it became much better, but he required switching weapons for teleport (Wizz spike + spirit), which was rather annoying to do for each group of cows.

With HOTO and Spirit used as a main set... he became hardly playable for effective cow runs (he needed WHOLE inventory of skillers and a torch to kill nightmare cows with one hit).

Final build was HOTO + Monarch with 4 RBFs, one-shotting cows was possible with: Torch, anni and 10 ele skillers (11 in the end). That gave him 60 FCR, Then I added one more skiller and switched one SOJ for 10 FCR ring to reach 68 FCR breakpoint. I have not tried how much inventory space would be saved with +6 hurricane, 2RBF pelt.

Updade Nr5 - Nova.... Necromancer

This was a my very first multiplay character and I completely forgot about it.
He can one-shot nightmare Hell Bovines with half-as.. uhmm with a really cheap build.

Skills:
Poison Nova: 20
Poison Explosion: 20
Poison Dagger: 20
Optional - Lower Resist: 1-20 (for when You are getting surrounded by poison immune mobs in Hell difficulty Stone Field / Tristram)

I just tried it with:
Helm: +2 necro + RBF (shaco will be great.. circlet +FCR even better (for tele)
Amulet: +2 necro
Weapon: none (would be great if he could use Occulus for Vigor.... might use Wind RW - but 20% FRW is not worth a SUR here)
Armor: none (Trang for FRW / Eni or TMs for teleport / FRW)
Shield: Homunculus (could use any shrunken head +2 necro or pnb or nova.. or Boneflame for 20 FRW)
Gloves: Trang (this may be the most expensive item here, unless one plans to use Eni/TM)
Rings: Bul Kathos x2
Belt: none (Mavina for 20 FRW)
Boots: none: (Aldur's for 40% FRW)
Inventory: Cube + Books of Indentity and Town Portal

I wonder... I wonder if with a complete Trang-oul set he could do it too..
YES! Full Trang is enough, not too fast, but works. Other items, like amulet, rings or weapon are luxury. (Those will increase his clearing speed).

It took about 2 seconds to kill a non-unique cow. (One Poison Nova cast - I was just running between cow packs, casting one nova, then going further)

Then I modified his items a bit:

Helm: +3 PNB +2 RBF
Amulet: +2 necro.. I didnt have a better one
Armor: Bramble 30% (That was unlucky..)
Weapon: Death's Web +2 -47% +RBF (52% total)
Shield: Monarch +4RBF / Homun +RBF (I haven't seen any difference to be honest)
Belt: Arach
Rings: 2x Bul Kathos
Inventory: Torch & Annihilus

Cows were dying in about 1 second (IMO its not worth all that cost).... but... he was able to one-shot even Hell cows (~2 seconds)!
He is very good, different than CE or Java, but from what I tested, he can reach similar clearing speed as those two on hell.

Updade Nr6 - Enchanted Bowzon

I have only tried it with:
- plain 6 socket Hydra bow;
- Hell Rack (despite being faster in theory is slower, so I did not even put RBFs inside of it) - Hydra was clearly better;
- Goldstrike Arch (for 50 IAS) - Hydra still better.
Have not tried:
- Hydra with mix of RBFs / Shael runes;
- Faith;

Skills:
Multishot - 23 (enough for 24 arrows);
Pierce - 9/10 - enough for 100% pierce with Razortail;
Critical Strike - Max (I wanted to increase damage as much as I could for Hell cows, but for nightmare it is not needed)
Penetrate - everything else.

Stats:
- Str: for gear;
- Dex: rest;

Items:
Head: Magic Coronet +30% FRW 2 sox (+9%/-8% total fire damage); - Could have 3 sox with 15%/-15%
Armor: Ormus: 15% fire (+20%/-3% total fire damage); - Could be 20%/-5%
Weapon: Hydra Bow 6 sox (+29%/-25% total fire damage); - Could be 30%/-30%
Amulet: Cat's Eye;
Rings: Raven + Rare with mana steal, mana and AR;
Boots: Aldur (40 FRW);
Gloves: 2 passive, 20 IAS;
Inv: Torch + Anni

With almost maxed enchant (I am lacking +6% fire damage on my enchantress - Ormus is 10%+3 enchant and Eschuta 3/14%) this amazons damage range was:

• Multishot: 8634-10k
• Normal attack (with Hydra Bow): 12k-14K

Multishots description states that it cuts weapon damage to 3/4, but it also works that way with elemental damage.. . Hell cows have 9'442 - 15'449 HP and 50% fire res, but with all 5/5 RBFs bowzon would have -50% enemy res (I had -36%) and a bit higher damage than mine (+65% vs mine +58%).... and slightly better enchant.

With this she was able to 3-4 shot hell cows in a single game (I hoped for 2 shots to tell You the truth, but.... oh well If I find someday 30/3 coronet, then I will try again, with best RBFs), with this she was matching not-best-geared (without griffon and Phoenix/4RBF Monarch) javazons clear speed.


SUMMARY: Generally, throughout all difficulties, Javazon is the best. With Auradin reigning in normal, dudu (with high cost) and Novamancer matching her in nightmare, and CE necro also matching her in hell.

• Nova soso

1. Normal: very good and newbie friendly (with comparable, low investment - loses to auradin, wins vs java and hurricane dudu);
2. Nightmare: deffinitely not newbie friendly, expensive , loses to java in both being cost efficient and effort efficient, wins vs auradin;
3. Hell: masochist friendly, expensive , loses to all commony used for cow hunts builds [Java, CE necro, trap-sin, .. even to chain light soso, hammer, but seems to be better than WW barbarian, rabies dudu, smiter (he loses really hard - Stormlash/Rift helps a bit here tho) and auradin - but this one still requires some testing].

• Javazon

1. Normal: very good (just after soso), newbie friendly - its actually a waste to use her on normal cows, as shes almost as effective on nightmare (level 80+, titans, razor tail, valkyrie wing helmet),
2. Nightmare: (together with Hurricane dudu) The best - Newbie friendly, highly cost/effort - effective, rather safe;
3. Hell: Together with CE necro: The best (even better with max enchant!) - both require more or less similar "minimum investment" (Titan, Razor, high FRW for java; source of teleport for necro - amulet (25 charges), circlet (25 charges), staff (33/48 - magic; 69 - Naj's), enigma/tm) and both grow similarly with better items.

• Auradin (Holy Freeze)

1. Normal: Best (can move fast with vigor in town, charge in maps, requires just a bit of investment - Normal Cows have up to 342 HP - lvl 27 holy freeze does 340-345 Cold dmg - so either get lvl 28 or 26/27+ cold RBF,
2. Nightmare: so-so, expensive , totaly not worth it,
3. Hell: Hell no!.. I mean .. loses to WW barbarian, but wins vs smiter (as long as hes not using stormlash or rift)...,

• CE necro

1. Normal - Not advised, not cost effective nor effort effective, requires same investment as for Hell (while casting Amplify Damage then Corpse explosion I had a feeling, that its a waste to do so.. .),
2. Nightmare - very good, but requires the same investment as for Hell,
3. Hell (together with Javazon): The best.

• Hurricane dudu

1. Normal - very good (with Teleport..) - comparable to soso (Nova soso can be - as it depends on player here - a bit faster, but takes more effort to constantly switch skills) slightly faster,
2. Nightmare - The best (together with Java) - expensive ,
3. Hell - I have not tried, but seeing how he was doing in nightmare, wont be better than necro or java.

• Novamancer

1. Normal - I have not tested (To tell the truth.. after Auradin, it seems a waste to go for normal cows with anything else);
2. Nightmare - The best (together with Java and Dudu) - newbie friendly , highly cost/effort - effective, can easily do it in Vampire form!;
3. Hell - Very good (at last!) - expensive.. .

• Almost max - Enchant Bowzon

1. Normal - Not tested
2. Nightmare - The best (together with Java, Nova necro and dudu), but annoying to play because of need of slave enchantress.
3. Hell - Good - ordinary cows were falling after 3-4 shots, but annoying to play because of need of slave enchantress (Java requires less investment for similar effectivnes).

KONIEC / THE END / KONEC / FINIR / FINAL / GALAS /ENDE / FINE / FINIS / КІНЕЦЬ / КОНЕЦ / 終わり / 結尾 !!!

PS. If someone finds something else, better than mentioned... don't PM me about it . I would probably end up hitting my head on the wall .