All of them generates 3x combos each target.

KoH - low damage, poison, 3 targets. 9 combos.

GsT - lowest damage, 6 targets in whole enemy field. 18 combos.

GC - medium dmg, 4 targets. 12 combos.

Basically, if you run poison tai or neurotoxin and you need the most amount of combos, tortoise is the best. For any other occasion, KoH.