I'm probably forgetting something but as far as notable exclusives go 360 has Halo and Gears, while PS3 has Killzone, Resistance, Uncharted, SOCOM, and MAG. Even Metal Gear Online, but... well, that probably shouldn't count. Don't see why you'd peg Xbox as the one with all the shooters.
As far as community, probably PC if modding takes off.
Honestly
PC>Xbox>PS3
You said it yourself... xbox has no good shooters...
PS3 won't have as many players since they have good shooters
PC will most likely be the "MLG" platformer, the fact that you can use a keyboard, xbox controller, or PS3 controller means that dedicated players from all platformers will be moving to the PC
P.S. I love xbox, but PC is a PC, not a console... It wins every time sorry