Romanian WASR-10:This is the basic entry level AK. These are generally ex-Romanian military, demilled into kits, and then reassembled by Century Arms for a fast buck. These are stamped receivers, and they are notable for magazine wobble, due to the fact that the stamped receivers are missing the pill-shaped dimples that generally stabilize the magazine in other stamped receiver AKs. Many if not all were also originally imported for single stack mags and then retrofitted to take standard 30rds. WASR-10's also have a reputation for often being assembled slightly canted, requiring the owner to drift out some pins and re-straighten the front or rear sight blocks. these are the AKs that feel rickety, loose and don't always accept mags smoothly. The bad ones are bad and the good ones are just fine.
Chinese MAC90's and Egyptian Maadis: Most of these came into America during the ban years, and are messed up for serious combat duty by their sporting features. They of course can be converted and modified, and when brought up to spec would make a pretty solid AK platform. Once and a while you can find them in a standard config, but those are more likely to be picked up by collectors.
East German: You probably won't see any fully built East German kits, but you'll find individual parts all over. The USSR pumped a ton of money into the East German military to show off at the front gates of Communism. Because of that, most East German parts and firearms are top notch.
Hungarians: The AMD-65s from Hungary are usually a mishmash of parts kits and weird feature options that no one would want like forward pistol grips and weird barrel shrouds that don't work. Usually built on NDS stamped receivers, they are ok variants. A good one would likely be a little better than a comparable WASR-10, but they usually need some furniture conversions to get them looking, feeling and running right. The SA-85Ms are better, and I'd think about one of these if I saw one and the price was right.
Yugoslovians: This is a pretty solid gun right here, with one major problem. The Yugos were all built with different sized parts than normal AKs, and so you cannot exchange furniture or certain internal parts. A little chunkier and heavier, they are a good gun, but the loss of flexibility on custom and maintenance parts sucks.
Bulgarians / Arsenal: My personal favorite and maybe the best AKs made. Bulgarians really have their stuff together and they put money into the design and the execution. Arsenal Co. is run out of Bulgaria, and has "loose business ties" to Arsenal Inc. in Vegas. The Vegas people import all these Bulgarian parts and then build them in Vegas to get around import bans. This is the only brand new manufactured AK you can buy, complete with 1 year warranty and a customer service line. These come sighted in (don't FULLY trust it), tight, smooth, and beautiful. The SA-M7 series are my favorite, but there are few other series that are great too. Only one or two models to avoid, and thats easy because they are the ones with long, long, smooth bore ends. They also make 7.62x39 Krinkovs which are the SMG sized AKs, which is genius. There is some conversion to be done, but you can buy them all finished too.
Saigas: These are commercial manufactured Russian AKs from the Izmash factory in Russia. To pass import laws these come in messed up, and have to be modified to be decent AKs. Luckily there is an entire culture of dudes out there that do only that. Saiga conversions are good rifles and one of the options I would be thinking about, except with the time, effort and money it takes, I would prolly just buy an Arsenal. Which leads us to our next variant...
Arsenal Saiga Conversions: Arsenal had the bright idea to buy up a bunch of Saigas and fully convert them themselves before sale. What we get is the SGL-10 which is a sporter that comes with the worst half of the conversions already done, but still legal for sale to Cali, and now the SGL-20, which is a fully operational, new manufacture AK built by master Ak builders using Bulgarian, Russian, and US parts on a real Russian receiver. This is one of the best things going for what it is and what it costs.