What M16 are we talking about (A1, A2, A3, A4?)
Their is advantages and disadvantages for both. As well, it depends on the combat.
M16 Pros: Accurate, lightweight, great bullet velocity (good for penetrating), 3 round burst (depending on which M16 your talking about) (great for open areas), range.
Cons: Non durrable/requires a fair bit maintenance, great bullet velocity (will go through you but it has no stopping power), 3 round burst (it's not great for enclosed areas).
AK-47 Pros: Large round (good stopping power), incredibly durable.
Cons: Innacurate.
The M16 is great for urban combat. Accuracy is key in these situations.
The AK-47 was fashioned for the hard Russian conditions and many other rough conditions. It's great for people who want to survive in whatever environment.
The AK-47 has been run over by a Humvee, and still fired. The barrel has been bashed with a hammer, and still fired. It has been completely submerged in water, and still fired. It has been completely submerged in sand, and still fired.
The AK-47 can be cleaned very easily (Taliban soldiers would run their boot lace down the barrel to clean it. It only little time to teach one how to properly clean it (I believe it's 4 hours). The M16 takes a lot longer.
I'd take the AK-47 if I had to survive in the woods/desert/whatever (just kidding I'd take my dad/my Winchester 94). I'd take it to arm guerillas and other non experienced fighters. But the M16A4 is better for the trained fighter with a little bit of luck (doesn't jam) and a little bit common sense (DO NO BURY IT IN THE SAN!). I can't choose.