Use these guns, one as primary, other in backpack:
MK16 SCAR-L is good close up, fires fast, and good damage.
M14 Good close up on shot guns, does great damage, great accuracy so you can also snipe with it.
See anyone far away, pull out a sniper/M14 and fire. If someone is close up, then use an assault rifle or smg (P90 is faster than a MK16 SCAR-L but horrile accuracy).