The M16A4 w/ red dot, deep impact and stopping power seems to be the most potent combination. I haven't tried the P90 or G36 much though and they seem to be pretty popular with folks. Swapping out UAV jammer, Dead Silence and a silencer on the M16A4 works well too. I can't resist the allure of 3x frags. Desert Eagle is the must have accessory.