Well, The Mayor from Buffy is one of my favorite villains but he would be kind of wasted without Faith around I think. And with no way to turn into the giant snake here it might be interesting to see how he settles in since I don't think there would be any immediate need to go killing him.
Possibly Shiba from Zombie Loan. Which has sentimental value to me because I loved the CR Euphie and Shiba had at the game Wasteland. I hear he stops being faux nice in the manga which...[I'm sure would be very cool, Dust!] interests me less. :(
I guess I like nice villains? The ones who lull you into a false sense of security.
Maybe someone from the X-Men would be the best for me. It could be interesting to have Magneto since he was the leader of the X-Men for my Kitty and obviously a bad guy for the other Kitty. I'm not even sure if he is bad or good right now in the comics since he kept going back and forth. Maybe he doesn't even have powers after M-Day. I'm very behind.