Dude i have the x360, ps3 and the wii... I think my wii got more game time then my PS3. Littel big planet i was disapointed with... Kill zone 2 is awesome but as far as FPS Halo > *.
All the other games i tried on PS3 are available on x360. If i rent a game available on both consols i will take the version with the most bonus; I'm talking about the new batman... the PS3 version has better graphics and more game play but thats the only game i can think of.
IMO what you should base your decision on is what your friends have. The awesome thing about these "new gen" are about online gaming. yes online gaming with randoms is ok but online with real friends you hang out with of even the people here on HAN is awesome. Most of my friends have the X360 that mean the when i buy a new game with multi player i always get the X360 version.
Also the updates are annoying as fuck with the PS3. I do admit that the PS3 is a better multimedia device though.