I'd like to say the Skorpion, but it just burns through ammo. I'll put my vote for the FAL. Yeah, it's effectiveness in CQB is limited, but you won't get caught reloading, and the damage can help you in a pinch. Put on a target finder and stock and perhaps quickdraw and you'll never get caught off guard.
Other than that I guess I would say MP7. It's a solid, well rounded weapon for almost any situation.