has to be Xbox 360...
It's a much cheaper console with better exclusive games for it (halo 3 & Gears of War)
Not only that but if your going to be playing online with various friends, then your going to want the 360 online setup, as it offers a partying system where 8 people on various different games can all chat to each other...
PS3's downfall is it doesn't have this and the only way to talk to somebody is in a private chat 1 on 1, or if your group of friends are all playing the same game in the same lobby.
Also 360's are just generally better, I've owned both and would pick my 360 above the PS3 anyday, the setup of the entire console is just so much easier and less annoying than it's PS3 counterpart.
My pennies worth there lol