Pigs are most effective but is more specialty solution as is velite gladiators. Puppies are certainly fun to send against eles.

Skirmishers are cheapest solution. Flame archers also good, just focus fire. Phalanxes work but are expensive. Use in combo for best effect.

Key is to stop the eles. Once they are immobilized, you will win the war of attrition.

The archers on top are annoying but just take the beating.