Well it's on opinion.
I for one would rather have the AK-47 due to how good I control recoil, though I do prefer the M4A1 as well.
So I'd be fine with either, but if I were to suggest one for ya, go for the M4, just as good, slightly faster thus evening out the damage difference.
I suggest making a new account just to test weapons and find out the weapon that suits you.