There is no "best" PS3 game out there, but the ones with the highest ratings that I recommend are as follows:
Assassin's Creed: known for it's amazing graphics, extensive world, and gameplay
Lair: Combat with dragons using your whole controller to steer your dragon
Mirror's Edge: Acclaimed as "The most exciting first-person adventure of the year" -EGM, Winner of the Best Original Game from Game Critics 08 Award, Best of E3 2008 from IGN, Best of E3 08 from GamePro
Devil May Cry 4: The fourth in the Devil May Cry series and personal favorite of mine. Great graphis and gameplay.
Links have been added to take you to sites that list the most popular games for the PS3 console
In my opinion Dead Island is the best, it depends on what you think of the game.
NHL 2010 by Ea Sports
Battlefield Bad Company 2
the ps3 is better, but if you want a family game system then the wii is the best.
my opinion resistance 2 and resident evil 5 Call of duty black ops is the best game.
NO it was aclaimed the BEST PS3 game!
the best ps3 game is What ever you think
Infamous 2
Ps3 or psp are the best.
In my opinion Dead Island is the best, it depends on what you think of the game.
uncharted 2
Demon's Souls
Killzone 3
fifa 11
FALLOUT 3
battlefield:bad company 2 is the best game of 2010 and the best multiplayer game
The best adventure game would ultimately have to be Little Big Planet.