Definitely 360. For achievements mainly, plus I do like the 360 controller more. Oh yah, downloadable content too.
Another thing, the PS3 will probably demand some kind of partial hard drive install which is kind of annoying. I know it supposedly reduces wait time and yadda yadda but I dont really notice any problems with wait time on my 360 games.
PS360 ftw!
Currently playing..........
Gears of War 2, GTA IV Lost and Damned, Little Big Planet (Yes I said I had no interest but my girl wanted to try it and we did and now Im hooked )