As a PS3 owner and having played both systems, I would go with the PS3 for a variety of reasons.
Online play. Better on the 360 with more capabilities, but that costs you 50 bucks or whatever a year. PS3 has good online gaming that is free, not to mention you can hook up a bluetooth headset instead of buying a XBOX headset. But if you are just playing with your friends, it does not matter. Though if you are playing random people online, XBOX is better.
Graphics. XBOX 360 has had better graphics in recent games because it was out for a year longer, thus programmers knew how the xbox worked and used it capabilities better than the PS3, which was new at the time. But, since the PS3 has been out for 2 years, programmers are now using the PS3 capabilities more, which are way better than the 360. PS3 uses a blueray format while the 360 uses DVD. In 2-3 years, you will really see the PS3 move ahead of the 360 graphic wise, which is the Microsoft is already working on xbox 720 or w/e it is called. PS3 is now going to have better graphics.
Controllers. Basically, they are the same. XBOX has the joystick where the PS3 has the d-pad and vice versa. It all depends on your preference. In games, in seems that R1 on the ps3 is used as RT (R2 on ps3) on Xbox. PS3 has rumble and 6 axis while XBOX only has rumble. XBOX seems to have a more sensative joystick compared to the PS3.
PS3 is backward compatible while some 360 versions are not.
Basically, PS3 is better because it is a more powerful system, and since the XBOX was out earlier it had a headstart and the graphics look better, but now we have reached the point where they are the same and soon the PS3 will be superior than the XBOX.