AR-15's shoot groups... usually with rounds touching and clustered together. AKs shoot patterns.
AK's always seem to get a bad rap when it comes to accuracy. Reality is, its almost always the shooter that comes up short.
I shot this at 200 yard with my SAR1 using its slightly canted iron sights and Wolf 154 grain SP's. The lower group was shot from a solid rest to confirm zero, the upper group from a cross legged sitting position at a steady cadence.
I shot these at 100 yards using my Saiga AK103K conversion with an Aimpoint ML2 red dot and Barnaul 125 grain SP's. Again, from cross legged sitting. Just for size reference, the "head" on that target is 6".
I also have a few AR's, some basic, some a little more precise. My Armalite M15A4(T) with a 1.5x5 Leupold on it, will literally shoot into the same hole with my reloads at 100 yards when shot prone off a bipod.
My basic guns shooting USGI 5.56, around 3-4" at the same distance, and very similar to what my AK's do. When you compare hits on target from both guns with red dot on them, other than the size of the holes in the target, you wouldn't be able to tell which one shot which.
One thing that needs to be addressed here too is the ammo. My Armalite will shoot tiny little groups with my reloads, but put that same USGI in the next mag, and it will rarely shoot under 2". Your gun, no matter how fancy, is only as accurate as your ammo. USGI is spec'd at 2-3MOA.
Same goes for the AK's. The right lot of ammo can make a major difference, and especially at longer distances.
Theres no doubt though, the AR's make the better "target" rifle when shooting at bullseye targets at known distances with known sight dope. The AK's arent trying to be a target rifle, like some of the AR's that often seem to get compared to them.
A lot of the problem with the AR/AK accuracy comparisons is, many people doing the comparisons arent using apples to apples when they compare. If youre a little more realistic in your comparisons, they really arent all that far apart.