Hmmmm, my first M16 was issued to me in '68. It had been properly maintained; the chamber was not pitted by corrosion and she functioned properly. When did you have time to clean it when you were in a fire-fight 24/7? I dunno, I was under seige for 30 days and managed to keep mine clean. I would see regular Army guys come back into compound dragging their 16s in by the sling, drop it on the ground under their cots and leave it there until it was time to go out again. It seemed there was always a bunch of smoke and booze in the barracks after a fight and lots of guys wanted to be friends rather than soldiers; the 'cautionary' 'ya'll oughta clean that 16 before you go out again' was often met with 'hey Sarge, have another hit'. There was a definite leadership problem in Vietnam, and malfunctioning weapons, poor battlefield discipline, high combat losses and demoralized troops with lots of bad memories (pstd) were some of the results. Lots of guys wanted 'buddies' rather than a good soldier next to them and when neither one of them could fight for squat or even remember their training, shoot for squat or used their M16 for anti-aircraft fire rather than the anti-personnel work they were designed for, they got killed. As a result it was always someone else's fault and some of these guys are still 'boo-hooing' over the mistakes they made 40 years ago and still think it was someone else's fault. Poor leadership, certainly but worse discipline following.
The AK over the M16 or the M16 over the AK - I prefer the 7.62x39mm round over the 5.56x45 but would not want to get hit by either. I wasn't concerned with collateral damage when we hit a target, be it a village or enemy position and the 7.62 AK round was quite effective when you had to shoot through things. The AK would work under any condition, not so with the 16.
I have a NHM91 that I installed a Krinkov flash hider to and pulled the thumbhole stock and the half log they used for a forearm stock and replaced it with standard AK furniture - it is rather accurate with good ammo and it has become my Appleseed rifle. I have hunted with it and it has a number of whitetail to its name. I have another Kalashnikov that I rarely shoot and although capable of laying down serious fire out to whatever your effective ranges are it is not capable of the 2.5" opensighted groups the longer barrelled NHM is capable of at 100m.