[Raellus]

It's well documented that the early M-16, relatively advanced compared to its contemporaries, was not ready for the battlefield (much like the Panther tank in WW2). By the 1980s, most of the kinks were ironed out. That's not to say that the later versions of the M-16/AR-15 are perfect, but there's a reason (besides marketing) that AR-15 "black rifles" are the most popular "assault weapons" on the US civilian market, and that military versions are used by armed forces around the world.

There are entire books and websites devoted to the Great AK-47 v. M-16 debate.

The arguments can be boiled down to:

Recoil/Accuracy: M16 (this is why the AK74 was created)
Reliability: AK (this is why newer assault rifles don't use Stoner's direct impingement gas system and instead use a variation of the AK's piston-driven system)
Weight (of weapon & ammo): M16 (also why the AK74 was created)
Ease of Maintenance: AK
Range: M16
Stopping Power: AK
Ergonomics: M16 (this is why the HK416 and SIG 716 & MCX pretty much copy everything about the M4 other than its operation)
Durability: AK

So it's pretty much a push, and the "winner" depends on what factors the individual shooter values more.