I've been bitten by the AK bug in the last year,so i've been doing a lot of reading up,asking questions on this and other forums. Though most seem to say all the wolf works fine, they also seem to have the most quality control issues, especially lately with the military classic. Wolf also seems to be considered among the dirtier burning ammo.
Golden tiger, which i have the most of and have fired the most of, seems to be about the most well spoken of x39 ammo around right now,hardly a bad word can be found about it, and i concur.It doesn't hurt that it is (or was) the least expensive,either. I believe Copesdistributing sells cases for around $185-190,delivered.
The Barnaul ammo is also well spoken of. They manufacture the Brown bear,silver bear,golden bear, and some just called "barnaul". I have some brown and silver stashed, and have had no issues firing either.
If you want to stash away some "nicer" stuff that's re-loadable, Aimsurplus,last i checked, has some brass cased,boxer primed, ammo for pretty reasonable prices. I've stashed a few rounds each of Sellier & Bellot,Yugoslavian Igman, and Fiochi.
Regardless of what you get,problems seem to be pretty few and far between. With this stuff, i'd probably recommend getting whatever's cheapest.