Modern Warfare 2 with around 750 hours. Not sure if it was the most fun since first 100-150 hours were just horrendous. Even after sometimes there would be a map that i just didn't enjoy. Playing with friends made it enjoyable and also i guess i got somewhat better.

I might have forgotten to mention that the most fun I've had with multiplayer on last gen was with Mass Effect 3. Single player might be controversial, but the multiplayer is loads of fun, addictive and rewarding. And frustrating too if you dare to battle in Platinum difficulty. I clocked in around 253 hours.

Mario Kart Wii!

My friends and I had so many epic local battles! I won most of them so that's probably why I enjoyed it so much, haha!

Definitely Dark Souls.

Forza 2

Black Ops 2 and Red Dead Redemption

Hard to choice betwen Valkyria chronicle, heavy rain & last of us, really loved all 3.

My games that i most played:

Demon's Souls
Killzone 2 & 3
Resistance 2 & 3
Dynasty Warriors 6
Resident Evil 5

Super Mario Galaxy, probably the game with the best level design ever.

XENOBLADE!!!