It depends on the games. I would say get a PS3 if you have a large PS2 library, get a 360 if you have a large Xbox library, but Sony got rid of BC, so that's no longer a factor for PS2 games.
If previous gen games aren't a factor, take a look at which system has the most games in your favorite genres and go with that one.
Both systems are fairly even when it comes to game performance and graphics, so that's a wash. I don't consider Blu-ray an advantage considering I want a cheap standalone player (I don't want to risk an expensive PS3 by playing dozens of movies on the drive). Blu-ray might prove to be an advantage storage-wise in the future, but very few games on the 360 come on more than one disk, so it's not much of a factor right now.
In the end, it's really about the selection of games.
