i would pick an M-16 over an AK mainly because there are now soooo many ar formats shooting different rounds.
examples:
DPMS makes a 300 SAUM
...nice. they also make it to fire...
.204 Ruger
6.8 rem
.243 win
.260 rem
.308 win.
Olympic arms makes a couple nice models also
.223, .243, .25 in WSSM, i've heard the .25 are nice
Rock River Arms has a model in .458....nice yeeeeeess

now i'm sure now a days you can get an AK in different caliburs but IMO you will never get the most out of the round in that type of gun. with the AR you know you are gonna get a accurate gun that can have hundreds of different mods to it.

go AR baby