I don't play it any more, but definitely MGS 4, probably my most played game ever. Spent over 2 years playing it, then had to go back when they added trophies.

I don't really know which game I have poured the most hours in, probably Skyrim, but most playthroughs is Uncharted 3, 4 or 5 full playthroughs, shit ton of replaying my favourite chapters, and a bit of multiplayer. Reason why? My favourite PS3 game, I just love it

Rock Band 2 maybe? Most of my PS3 games were single playthrough games.

I think COD4.
It was the second game I had on the PS3 (behind GTA IV) and I played it for aaaaaagggess.

evil activision decided not to honour one of the best games of the generation with a trophy patch =(

It is easily Battlefield Bad Company 2. By far my favorite competitive MP of its GEN. 500 or so hours and counting.  Also one of few platinum trophies I have.

The top 3 (don't know the exact order)
- Resistance 2 (online 60 players matches mostly)
- WWE 12 (local multiplayer, probably WWE 2K14 will get as much hours as this one)
- The Last of Us (online multiplayer)

In raw play hours... hard to say...prolly any Shooter of any Fifa I played with friends...

Prob Killzone 2 thanks to its multiplayer

LittleBigPlanet easily! The game has literally infinite replay value! So much so that I haven't yet felt the need to get LBP2! xD

GT5 because there is no room this generation to play GT6 until surpass GT5...

But GT7... OMG.