One of personal favorite "evil" units combos is a Lich as a leader with Phantoms as his escorts. You get a unit with Low Sky movement(mobility) A boat load of attacks, and if for some reason you are fighting a cleric class and they successfully turn all of your undead, the Lich is so self sufficient that you can destroy the unit anyway...Then you can just recruit new undead from anywhere on the map. I love the Lich.
However, I would def. agree that the Princess is a far superior unit. She gets 1 Hit All Holy based attack in the back row, she can recruit angels which are a great class, and even the Faerie that has its merits if you can class change it quickly. Not only does she have that going for her, but because of her awesomeness she grants each unit an extra attack, including herself. Awesomeness. It is rather hard to find the crowns though, but I do know of a sure way to get one in the middle of the game if anyone is interested. I can PM you or vice versa because it is a huge spoiler that I don't wanna write in here.