I think it's impossible to compare the two...
The Wii is great for its local multiplayer--there are countless games that you can play with your family! Nintendo makes a lot of unique games that are exclusive to their consoles... One could argue that their first-party games are better than the Xbox's. The Wii remote takes some getting used to, but when you do, it makes for a very unique way to play!
The Xbox 360 is more like a standard console, and that's not a bad thing at all! The Xbox has a simple controller and a better third-party library. Also, the Xbox can handle HD graphics unlike the Wii. I find this console is great for single player games, and for going online to face off against other people from around the world.
If I had to choose one over the other, I'd probably choose the Wii, but only for nostalgia and the fact that I've owned my Wii longer. The Xbox is still an incredible console and ranks up there with my other favorites! :)
I love how absolutely random and funny they are :D
I love how friendly they are X3
I love to read their forum posts and opinions on stuff :D