I'd go for an xbox 360... Now be prepared to here a long boring story of my life with my xbox...
I brought my 360 in March this year, and I'd thought about it long before I brought it because I was considering the PS3.
Thoughout having owned a 360 I've always wondered whether or not it was a good idea, but the great selection of games that are comming out for the 360 has made me a lot happier! The only thing that will make me buy a PS3 now is Metal Gear Solid. I've played all of the others hundreds of times, and love them all, so I will miss it dearly...
Anyways, yeah... buy a 360