I have trained extensively on both in my prior life. The AK is a vastly inferior action for urban combat relative to the AR, primarily because it is bloody slow to use even in the hands of a competent soldier. An AR15 can put more rounds in more targets faster in the hands of a competent user than any assault weapon of its time, which is the genius of its design. It allows extremely rapid and precise target engagement, something that I have learned to appreciate. Incidentally, these weapons (and several others) have been put through performance metrics that measure this type of thing, and I have been involved in some such studies, though a cursory googling is not finding much in the way of published data on this point (not surprising, being pre-web studies). If the primary objective is to hit a lot of targets fast, the AR is your action.
As an aside, we never had any reliability problems with the AR actions out in the field, even when pretty filthy. But then, I never used Viet Nam era ARs with the defective Viet Nam era ammo that gave them their (undeserved) reputation for unreliability.
On the other hand, the reputation for poor accuracy of the AKs is not entirely deserved either. The Finnish Valmets (excellent AK actions), for example, have a rack-grade accuracy that easily rivals the M14, though neither is as precise as the AR action (which is intrinsically far more precise than it needs to be for a military weapon).
Dead on, and the single greatest reason why 556mm rifles remain dominant.
Those who do not appreciate this fact, advocating a return to the battle rifle, do not understand the nature of modern infantry combat.
It's not about penetration, range, or even lethality - hitting first is paramount.
The AKM is a fine rifle, for the poorly trained and undisciplined fighter. It's an also ran compared to the modern M16 series.
The M-16 has an extremely high rate of fire on full auto (able to empty a full clip in 1/2 second). That's why later variants have a three round limiter. Thinking being that a squad of soldiers firing in concert can lay down much withering fire, that opposing forces have to go through (and for a longer distance), than with other weapons. There is a certain psychological issue at play here too, the enemy knowing that they have to withstand accurate fire from 200 yds out (they will pay dearly for any assualt).
Moreover, the M-16 is a high-velocity round. The instructor told us that when you fire the gun by the time you hear the report, the bullet is already 100 yds down-range. Kinetic energy has a square in the equation. You'll never find a spent M-16 bullet because of this reason. An M-16 round that impacts anything substantial is going to shatter. So an opponent may get hit in the shoulder, but fragments could be exiting anywhere (knee for example). A few M-16 rounds are most certainly lethal. One well place round shattering and making sausage inside the rib-cage is going to be lethal also.
I also liked the virtually no recoil thing the M-16 has going for it.
The AK-47 on the other hand is a much heavier round. Furthermore, it has a tendancy to tumble in flight so its accuracy will not be as high as the M-16. However, a tumling bullet does have a tendancy to make a rather nasty wound.
All the foregoing being said, the M-16 is not really intended to be lethal. If lethality was the intent, the Army would be using WWII era .308's Its a logistical issue, the M-16's prime task is to overwhelm the enemies war machine with wounded casualties. A wounded soldier does three things, it can make them outright non-combatants, or diminish their fighting capablility, and they will drain resources that could otherwise be expended on the war effort. No army can afford not taking care of their wounded, not so much from a humanitarian perspective but one from a morale perspective. Soldiers that realize their forces aren't going to take care of them if they get hurt, may choose not to fight. Again, if the intent was to kill, the U.S. military would be still using the .308.
At least that's what was taught to us troops in Reagan's military. I'm sure that the war that was being planned for then is different than what's going on now.