Depends on the game and map really.
In halo, I go all out tank, and just decimate people with heavy weapons, and precise headshots from close range.
In call of duty, I play more stealthy and sneaky, constantly taking flanking routes, and using the ninja and cold blooded perks to my advantage to surprise enemies, and take them from behind.
On maps that are mostly open, or long range, I'll pull out the sniper, and get some headshots in.
It really depends on the situation though, and what my team requires at the time. I can play various styles, and adapt my play as necessary (as any good player should).