Pistolero, you are indeed right, sir. When it goes to real-life standards, accuracy, and precision is all you need in a gunfight.
Indeed. War isn't just about who makes the most awesome kill. War is about incapacitating the enemy. Shoot someone in the leg and that guy won't fight no more. That's why precision over power. The only downside of 5.56mm compared to for example 7.62x39 is that it can't penetrate walls and defenses that well, and I think even flak jackets can fend them off from a distance, and perhaps helmets.
I really wouldn't pick for example an M1 Garand or lever-action guns as MY gun, as they're obviously ages old and not as reliable as modern weapons.
Of course if I could choose from real-life guns, I'd go with the http://www.majkasvihoruzja.com/files/slike/puska-sako_rk_95_tp_2.jpg assault rifle as it's the one I've got training for and it's the most accurate and stable of the AK series. Easy to maintain, only downside is I think is that it's expensive to produce, but that's not a problem for an individual soldier.
But then again, I have a mod to give me that gun in-game so I guess it counts

Extra accessories include scope, silencer, bayonet and 'nade launcher.