Xbox Live looks golden compared to the shitty service Sony offers
Multiplayer is best on the PC and I think it should it stay that way. And yeah, I frogot about Timesplitters, that is true.
But another big reason for X360 (for me anyway) is Bioware. PS3 always has some insanely good RPG's. Xbox usually gets some good stuff too, but few and far between.
To name a few good RPG's on the Xbox, new and old:
Knights of the Old Republic
Knights of the Old Republic 2
Jade Empire
Fable
Oblivion
Now, ALL of these games are available on PC, but they all perform like bad ports IMO. The controls and movement are all designed for a controller, so they're no good on a PC with a mouse and keyboard.
Also take note that 3 of the 5 listed are made by Bioware
Fable is a sort of in-between option, as some people really liked it whilst others couldn't stand it. I thought it was good but short.
Either way, PS3 is the third party right now. They might take over, but they need that killer game first. And right now, they don't have it, and I don't think Killzone will be enough to do it.
And Nem, in response to the Hl2 > Halo statement, I sort of agree.
There's no lying that both of the games were megahits that really had a major impact on the genre, but they did two different things.
Half Life 2 (and even half life) changed the way we play first person shooters on the PC. Not only did the game have a complex and always-unfolding story, it also had an amazing engine to back it up. Furthermore, Half Life 2 has spawned so many other games (Counterstrike, Team Fortress, PORTAL!!!,Day of Defeat, Garry's Mod) that have also become incredibly successful on their own. Half Life 2 has done great things for the PC.
Now Halo has done it's own part. Off on the Xbox, it has once again brought the joy of the first person shooter to the masses. It basically started where Goldeneye 64 left off, and unlike the crappy follow-up Bond games, the next games in the Halo series didn't suck major balls.