Death Structures

Ghost -> Vampire -> Devil - in my opinion, this is the best!

I agree, but poisonous creatures are also good. And they have more HP - 100, they shoot poison, and they are a real nuisance. It's good when the hero is a demonologist and knows magic. Nature - 4th level and demonology with death magic - 4th level. He will be able to summon them. But vampires are also good because of their vampirism + they fly + they look stylish, unlike the samurai in Heroes 5:D