Wyverns

But electricity is actually more useful.

I don't understand why electricity is more useful (except perhaps against Necropolis and partially against Academy), the damage doesn't increase, but is distributed among all enemies standing in a group, so it seems like you hit, but you don't really kill anyone, and you even take damage in return from a stack that hasn't lost many units. Poison may be weak, but it ignores armor, does its thing for 3 turns, and the retaliation is much smaller. Paoka are great because of their ability to devour, they saved so many almost lost castle assaults...