Berserker recommendation

Lu bu is solid boss buster if you need farmer then go for kiyo or eric

all 1*-2* berseker wont work unles you grail them, they die to fast and give low damage.( i grail asterios to 80 and skil 10-10-10 and i actually love him)
kiyohime = wave clearer. the only think that she can give is her np spam
tamamo cat= i dont think tamamo is good if you campare her to other 4* servant, she kinda lacking damage, skill and her np have big drawback
lu bu = Lu Bu is a Servant with incredible damage potential, but a huge amount of support is needed to let him perform at his best.
personally i will chose lu bu or kiyohime

IMO Kiyo is great for farming exp cards if nothing else. There are probably faster options, but Kiyo can wipe the final wave if you spend the first two charging her up and chaining Mash to the purpose of keeping her alive.

I kinda disagree with lontong's assessment on 1-2* berserkers. Some can deal more than enough to blast through weaker waves (around 30k?), even without any grails.
Spartacus and Eric are both great options, if you can NP charge them instantly, that is (usually a support Waver + 50% Starting NP CE). But i guess that is the case for all AoE farming type Berserkers. I do rate Spartacus quite high because of his own Charge skill (Lvl 10 is optimal, you can get away with less depending on the CE).

These two need a bit of investment, though. Without some levels in skills, ATK Fous & Interludes/Skill Strengthenings, things can get really awkward. Also, besides shooting their NP there is not much they do, so there has to be a plan how to deal with the remaining waves.

Eric can be your last man standing zerker for a while.
Asterios for massive debuffer or stall team member zerker.
Darius III is like or similiar to Eric.
Tamamo Cat for single use NP or use her as a non NP hitter.
Caligula is a Buster Crit Zerker.
Spartacus is pretty Durable for a low rarity zerker.
Lu Bu is a OHKO zerker A.K.A One Punch.
Dr Jekyll is a zerker + Assassin, he can switch class.

For me, i'd recommend Spartacus for more durable zerker and useful for daily farm also Caligula or Lu BU if you can cover or protect him.

Caligula has a unique playstyle and he is one of the suitable low rarity zerker for Buster Crit Option, his only drawback is the lack of Survival kit but with the help of tank/Supp he can be your main damager.

Lu Bu, One Punch Man Berserker from low Rarity pool if you can cover him well, then victory is truly guaranteed to you.
His NP damage is on par with some 4* and 5* servants.

Zerker is one of the best medicine, when you're in doubt just use zerker.

Kiyohime is perfect to farm hands. Also, Stalking+FlameColored Kiss maxed+NP5 make her hit bosses kinda hard for an AOE (still not optimal).

Lu Bu is ST (optimal for boss killing),NP ignores def ups. NP5-ing + Kaleido/Sakura 60% NP bar CE on him and a Georgius taunt to help he survive for some time is the way to win (or at least weaken) against problematic solo enemies.

Eric is budget Zerkalot; AOE, buff his attack b4 firing NP, if you have Halloween Princess/Holy Night Supper and a Waver friend, he can do a lot of damage. And he has gutts and HP up, so he can survive a little more than Zerkalot, at the cost of not critting neither generation tons of stars on his NP...

Asterios is good for his NP debuffing.

TamamoCat is worse than post-ST quest, NP5 Kiyohime on everything.

Level Kiyo/Eric for farming, Lu Bu for ST dmg, then move to Herc if you get him.

For farming kiyo or spartacus.
For st, lu bu.
Alternate option, jekyll and hyde. You must have the right craft essence, level his 1 and 3 skill to at least 6, have a good star genner, and a support to keep him alive. Can do herc level damage not including np. His assassin shell can keep him alive until the last wave.