A lot is said about the weapons by looking at the safeties:
When you take the AK off safety, you're first placed on "auto". The user has to take an extra step to get onto semi; you get the feeling it was born to spray.
Doing the same thing with the AR first puts you on semi, where the weapon was intended to reside, mainly.
Even so the M-16 is vastly more controllable on full auto due to it's straight line from muzzle to stock design, smoother gas system and recoil buffer.