Get 360, I've got both. The Wii is good, but more of a party multiplayer platform.
Graphics on Wii can be a little disappointing, and there is no HD output. This doesn't matter so much for party games, but with 1 player games like Zelda I'm a not happy with the fuzzy graphics (it's still a great game though)
I have a360 myself.
However it depends on your game prefrences, and your family.
The wii is more fmaily orianted.
However 360 has the big games, and is more adult themed. (although it does have its few kid games)