360 by farrrrrrrrrrrr.

As WW stated, if you have a party house or whathaveyou, then the Wii is probably your better choice since they have a lot of games geared towards groups.

With that being said, the 360 fucking dominates. I bought mine around February and it's been turned on pretty much everyday. Right now, I'm heavily addicted to Halo 3 on Live (I'm almost ranked a general - to you Halo nubs, that's the highest rank you can get). Plus, the 360 has a TON of games that appeal to every group. There are some decent RPGs out there, definitely some good FPSs, and as you mentioned some pretty good sports games, among others.

Overall, the 360 is the way to go.