PC version's better.
I mean come on, the PC version has mouseaim, and it can run at 60 fps! The Xbox 360 version never goes faster than 30 fps. However, the graphics on the 360 port are really great. Usually when a PC game gets ported to a console, the console version always has worse graphics. Not so, here. Okay, true, I can't run my PC version on the highest settings, but the graphical difference is negligible, I think. I also haven't encountered any slowdown on the 360 version either, which I do occasionally suffer on the PC version.
The controls aren't as good, I know. However, aiming with the joystick isn't that hard on a 360 controller. Sure, it's not as precise as a mouse, but I find it easier to aim precisely with a 360 controller than I do a PS2 controller. However, I find selecting weapons is harder to do on the 360 version than the PC version. At least in Bioshock, the game pauses when you switch weapons. Not so in Half-Life 2. Bummer, man.
By the way, I'm stuck on Episode Two. Fucking Striders, I swear. If I'm lucky, I might have the game completed before school starts, provided I don't get distracted.
Shiny object! *gets distracted*