As I don't have an Xbox 360, I'm buying KZ2 and Res 2.
Sales:
Gears 2>Resistance 2> Killzone 2
(I guess the number four craze is over)
Graphics:
Killzone 2=Gears 2=Resistance 2
Gameplay:
Res 2>Gears 2>KZ2.
Well, KZ2 isn't really competiting with them, it's coming out 2 months later.
EDIT: As for metascore,
Gears 2 = 91-95
Resistance 2 = 92-96
Killzone 2 = 90-95
So all really close, all really good.