Left 4 Dead

I don't know what platform to get left 4 dead for, its between 360 and PC. Here is the arguments I've come up for both sides. The arguments pretty one sided but the two arguments are pretty big points.

Xbox 360
    Split screen co-op (So my brother can get in on some co-op)
    My friends are leaning towards 360 (and I want to play with my friends)

PC
    360 is not supported for updates and patches (I learned my lesson on Orange Box)
    No mods for 360
    Better graphics
    Preferred control scheme
    Cheaper

Oh an I just got a new headset for 25 dollars and the mic is clear and the audio is great. I recommend it. It is the MS LifeChat LX-3000