Yeah, since you want just one, I'd have to go with 360. Only because Wii doesn't have too many good games yet. Though, Godfather Blackhand Edition is a great game for Wii. Nothing quite like motion controlled extortion. But, 360 has more games right now. So you have a better chance of finding one you like. Ehh, screw it. Do whatever you want, what do I care?

Edit:
Agh, your page raped my caps away.