PS3 hands down...
it is backward compatible with some games...not a lot though, mainly more recent titles..
Graphics are superior, just depends on the game as some dont show as much as others...
I worked for Krome Studios...dnt know if anyone knows of them, but it was pretty much PS3 for the win, i worked on 'Hellboy: The science of evil' which was on both 360 and PS3 and the PS3 did show clearer crisper graphics.
360 controllers are a cheap rip on Playstation controllers IN MY OPINION...
not to mention the PS3 controls are much lighter (obviously because they removed the vibration function), which is awesome, and they also have the six-axis function, which isnt that much of a major feature but is kind of cool (im sure it could come in handy for those who like to tilt to the side when playing racing games etc...)
as was covered 360 has more next gen titles, but a lot of the best games are PS3 only...well my favs ie...Final Fantasy, Metal Gear Solid 4, GT 5... the list goes on
360 is a good console none the less, but i think the main reason a lot of people (and this is going back a fair while) chose 360 over PS3 had to do with the fact that sony kept pushing back the date, which as im sure evry1 will agree was freakin annoying... and im sure this cost them a lot of support as the hype died due to the constant promise that it would be out and then knocking it back again...
any how thas my 2 cents...(more like $20)