Xbox 360. If you can't afford xbl now, save up a few dollars here and there, because you can probably find a xbl membership card for 35.00 for a year online. I got mine on amazon about a year ago for that much. I don't know how much they are now.
My point being, I have both ps3 and a 360. I play alot of sports games and nothing beats the atmosphere like xbl. I use to buy sports games for both but now exclusively for 360.
Don't get me wrong. I play the shit out of my ps3 as well, but when it comes to sports or fps, 360. Now the people with a ps3 or a wii will tell you ps3 strictly because they hate 360 (probably never even picked up a 360 controller). PS3 owners will say that because they hate the 360,Wii owners will say that because they'd rather see people buy a PS3 than a 360.
Fact is, based on what you like (games wise) i'd go with xbox w/xbl. If you'll never pick up xbl then get a PS3. Even if you decide that you want a ps3 for the blu-ray (Hoo-ray HD DVD is dead), there's 1 problem, the 360's coming out with their stand alone (according to them, affordible) blu-ray player.