Just got my FFL and I'm looking for the right stuff to keep in stock.
I'm not an AK guy, been more into the VZ-58, so I thought I should ask the experts.
Assuming 7.62x39 caliber, which magazine is the "best", "most reliable", "most desirable", "best value", etc you enter the catch phrase.
Obviously, I won't know which specific type of AK the customer will have. Is there a most universal magazine?
Looking for 1, maybe 2 magazine types to keep in stock.
Thanks!

I'd recommend you check out this recent thread:

Best 7.62x39 mags going at the moment?

If you can figure out how to get them, I'd carry the Bulgarian commercial steel mags and the Bulgarian commercial polymer mags with steel reinforcements. Here are the GunMagWarehouse listings for reference:

Bulgarian AK-47 7.62x39mm 30-Round Steel Magazine

Bulgarian AK-47 7.62x39mm 30-Round Reinforced Steel Lug Polymer Magazine

They're reasonably priced, good quality, and they have the look and feel of "classic" AK mags.

If you can't get those (I'm not sure who imports and distributes them), or even if you can but want to offer U.S.-made magazines, I would recommend these from XTech and Magpul:

XTech MAG47 - 30 Round AK47 Magazine

XTech MAG47 MIL - 30rd AK47 Magazine (more expensive but stronger steel reinforcements)

Magpul PMAG 30 AK/AKM GEN M3

Bulgarian Circle 10 and surplus steel mags are always great, but they're expensive (in the case of the former) and harder to come by these days (in the later case). Hope that helps!

My favorite magazines without regard for cost are Circle 10's. Steel milsurp is always good to go if you don't mind the weight, cost varies in the current market.
My second favorite widely available polymer mag is the Xtech, they are very durable, just a bit on the thicc side.
For pure value for the dollar I think AC Unity is the best. Definitely not as durable as Circle 10 or Xtech, but hard to beat for the price, they make a great range beater mag.

Any of the military surplus is always my first choice. Not sure what the second choice is anymore

Surplus steel mags are always my first choice, but I'm not sure that's a viable option for the OP, who is a new FFL trying to stock AK mags for his customers. Surplus mags have gotten pretty rare, and I suspect it's one of those things that long-time dealers may have access to through importers, customers trading them into the store, auctions, etc. I'm not sure how a new dealer would develop a source for surplus AK mags without buying them from another dealer and then having to jack up the price on them. The small shops that I've checked in the last few years, and even dealers at shows, tend to have only a small handful of real surplus mags that they got from somewhere, and the rest are current production commercial Korea, Croatian, etc.

I think a new dealer like the OP will need to start with the best quality commercial mags he can get and then maybe sell a few surplus steel mags here and there if he can find them. To have a regular stock of AK mags that are consistently available for his customers, he's going to have to go with something other than surplus mags.

Were I in the market for more, I would agree, with Soviet/Russian phenolics ("bakelite") second.

As for the average consumer, some will want "the best" and some will want "the cheapest". If it were me, I'd probably try to stock a variety to cater to everyone.

I'd say the best options right now are either the Croatians from PSA for $12.99, or the new KCI mags that Global Ordinance has for $7.99

Croats are probably higher quality

The Croat mags are just as good as any other euro mil surp AK mag IMO. Others have complained of fit issues, but I haven't had any.

The KCIs are slightly thinner metal, work well, and are a damn good deal at that price

These KCI mags are much tougher than the old ones that gave korean AK mags such a bad rep. The old gray finished ones were around 8 ounces, these are a shade over 10.5 ounces.

Just saw the korean mags are on sale for 5.99 5.99 ak mags