I have both an AK and SKS, and I've never noticed a difference in any way between the brands easily available and cheap for me: Red Army Standard, Tula, Wolf, and Brown Bear. I'm not a good enough shooter to see a difference, and I don't think the guns are good enough to show any difference.
I haven't ever had any malfunctions of any kind with either gun using the previously mentioned ammo.
I've heard that TulaAmmo is not as good or lower quality, but that hasn't been my experience. I don't remember where/when/who said that.
I do remember watching Nut'n Fancy shoot a sub moa group (I think) with a Ruger American chambered in 7.62x39. I want to say he was using Wolf. Of course, that isn't typically, and says more about the gun than the ammo in my opinion.