Wyverns

I don't quite agree. I always build the dwelling for Wyverns last, as it's expensive and not very effective. But to say that it's a completely useless unit is nonsense. As for choosing between Paokai and Dark units – against Mages, Elves, and Humans, I take Paokai to deal with ranged units using electricity, and also against Necropolis. In all other cases, I choose Dark units.