Vampires!! Their skill-tree is much more interesting with more fun things to do. With casters it's too easy to learn all the magic there is to know, and with vampires it's more work so it feels more rewarding to accomplish power as a vampire. Also with casters it's way too easy to become one. Sure, vampires can be equally "easy", but there is no "meet the vampire sire" headquarters to turn themselves, no, they must weasel their way into the lives of some vamp they meet and find out if that vamp is powerful enough to turn them, which is such an important part of the storytelling aspects that simmers(who actually play for game-play and not just building) can enjoy.