Probably Demon's Souls (psn) Uncharted 2(psn) and bad company 2 (psn

Most played............ in no particular order.

WWE Smackdown v Raw 2007 (approx 500 online matches, Won 260 lost 240)

Virtua Tennis 3 (Approx 715 online matches, Won 510, lost 205)

Ultimate Mortal Kombat 3 (approx 1320 online matches won 645 lost 675)

Ridge Racer 6 (500 online races easily)

Tiger Woods PGA Tour 06 (around 370 online matches before EA decided to close the servers..... grrrrrrrrrr)

Street Fighter IV (over 400 legit matches online)

Gears of War 2 (countless amounts of horde matches)

Stranglehold (god knows how many matches, but around 700 kills/deaths combined)

Left 4 Dead (played around 400 verses matches)

Halo 3 (around 200 online matches)

Streets of Rage 2 (easily 200 online co-op story sessions)

Well, overall, i would just give the crown to Virtua Tennis 3 as my overall most enjoyed online game this gen (some of the doubles matches were epic)

Honourable 3 mentions go to Streets of Rage 2, Ultimate Mortal Kombat 3 and Left 4 Dead.

Mind you, there is one game coming out later this year that has every chance of even eclipsing Virtua Tennis 3...... and that game is.......... Guardian Heroes.

All XBL titles.

Uncharted 2! best online game ever, only gonna be topped by Uncharted 3 wich is looking amazing!

I've only had PSN for just over a week but so far my best memory ocurred today, being a level 8 and managing to take out 2 level 50's with just the square button. I was a level 1 and now I am a level 8 and didn't play for long.

COD: Modern Warfare 2 - easily my most played game online
Soul Calibur 4 - I fed off kicking the asses of the hundreds of button mashers that played this game

No other games have interested me that much online... kinda sad really.

Xbox                               
Modern Warfare 2
COD: Black Ops
Gears 2
Forza 3

PS3
Uncharted 3
Killzone 2 & 3
Fifa 10

Halo Reach has been my most favorite game to play, me and my friend have put more fun hours into Reach than any other game we've played.

On the original Xbox, it was Halo 2, Burnout 3, Tony Hawk's American Wasteland, and Star Wars: Battlefront 2. Had a lot of fun online with all of them.

On the 360, it has been Halo 3, Halo: Reach, Battlefield: Bad Company 2, and Gears of War 2. Played them all a hell of a lot, although with Gears 2 I was never really that great at it haha.

And for the Wii (although not asked), it was Medal of Honor: Heroes 2 and Mario Strikers Charged. Played them a lot because connections were good and I was damn good at them haha.

too many to even count

but demons souls on psn takes the cake with killzone 3 in close second

Xbox 360:

Left 4 Dead 2
Gears 2
Reach

Playstation 3:

Battlefield: Bad Company 2
Warhawk
LittleBigPlanet
Killzone 3

I've probably had the most fun with Bad Company 2. It truly is an amazing game. Left 4 Dead 2 is a close second. Playing as zombies never gets old. I've probably played online more on LIVE. That could change with Starhawk and Battlefield 3.

The first time I was invaded in Demon's Souls was by far my single best PSN related experience! A half-hour battle that resulted in victory! 'Twas epic indeed!