It's been a while since I have played an FPS but I typically switch my role depending on the game.
In Halo 2 I was a charger, but was a ducker in BF1942/2142 since there's just so many ways you can get 1-shotted. I played sniper in Medal of Honor:Allied Assault, had this one spot on Omaha Beach and I'd rack up dozens of kills before anyone found me. And in UT2004 I was the worthless player who spent the whole match trying to pancake people with the manta.