Your favorite hero...

The demons look quite decent, but the necromancers... well, they're not that great. And their abilities aren't very impressive either. Arantir turned out to be the strongest hero of Necropolis.

I wouldn't say so. You're forgetting Markel, Kaspar, and another guy who multiplies ghosts on the spot where enemies die.
My favorite hero is Wingael (from the standard heroes). From the campaigns, I like Railag (the master of initiative – that's a great thing!).