I've toyed with collecting Undead for Warhammer in the past, and every time I always do the same kind of army. Big powerful vampire, minimum number of token heroes, and endless zombie hordes!
It's not really competitive*, but it makes for a very fun game and is very fluffy. I've carried this over to my Mordheim warband, and with the consent of my opponents I have one vampire, one Necromancer, and endless zombie hordes! My objective each game will be to get as many zombies killed (re-killed?) as possible, and generally have lots of fun.