M-4 Carbine (.223)
Mosin-Nagant (Russian WWII infantry Rifle) (7.62x54)
SKS (7.62x39)
But of the three the M-4 is the most fun and impressive to shoot
I don't agree with the idea that an M4 is impressive to shoot. It has the feel of an air rifle.
It may seem light like an air rifle but when on patrol day in and day out you want something light that can still lay down an impressive amount of fire power