I have both systems for different reasons..
360- If I want great games, an excellent line of downloadable games, plenty of online play I go with the 360. The online service for XBOX called XBOX LIVE has a charge based on different plans (pay by month(s) or year) and there are more online gamers on 360 for such games as Gears of War 2, GTA4, Call of Duty, etc..
If you do decide to go with the 360, I'd get the Elite and not mess around with pricing. Far better system with an HDMI input and better internal cooling. I have one of the first series of 360's that had the 3 red rings of death and the faulty drive that scratched games but XBOX took care of the problem 3 times by sending me 3 different systems. Friend has had his Elite with no problems yet. Great wireless controller
PS3-I wanted blu-ray for our flat screen and it was amongst the cheapest players at the time. The online gameplay is okay. The browser on the PS3 is slow and sometimes won't display pages well. It'll display camaro5.com pretty good. Pretty reliable system, no problems except for the online browser freezing. Controller is wireless and a bit awkward in feel but a good aftermarket helps. Smooth graphics.
In my opinion get the 360, you'll be ultimately happier if you are a true gamer that likes to play awesome games
XBOX live ID: Edvalian