It depends on what you're into. I own both the xbox 360 and the ps3. Ironically, the xbox is in for ring of death repair right now. More ironically, I think I would still say I play the xbox and like it more than the ps3. That being said, the ps3 is the better system in terms of hardware, speed, picture, it's a hell of a lot quiter, its a sexy sleek black, etc, etc...
I love them both but the online versatility of the xbox live has the SHIOT kicked out of ps3 online. This is where everyone points out that ps3 is free! Agreed, however, I'd rather pay $50/year for all the options I get on the live. You can do so much with the live service esp. as it relates to finding friends and starting up games with a group of online buddies. The xbox (pro) is white (ugly as hell, but I used a specialty plastic paint to make it black - looks WAY better). It is loud. If you get stuck with an older manufactured one, you'll proabably have to send it in for repair at some point. All that being said, I still like the xbox better for gaming, esp. online. More games... more xbox folks online (IMO)... SEEM to have a bit better selection on games...
HD on the xbox is good but doesn't touch the blu ray capabilities of the ps3 which is why I had to have both. I primarily use the ps3 for watching blu rays and the occassional gaming. If i'm bout to roll up and play for hours... xobx is coming online and I'm hitting up my homies! I talked a friend of mine into getting the ps3 b/c he wanted the "better system". Hardware wise, I think the ps3 is the "better" system but he never even plays his anymore other than watching movies. I think if he had an xbox, he'd be online a whole lot more. My xbox has seen WAY more hours than my ps3.
As for a game... I bought gears of war with the xbox and played it constantly until gears of war 2 came out. Now, I play it constantly and replay value is very high b/c they keep coming out with new downloadable software for the game to keep it fresh... it's hella tight!
Best of luck~ SMOKE