SAR differences are in caliber. SAR-1 is 7.62x39; SAR-2 is 5.45x39, SAR-3 is .223. The WASR is 7.62x39 whose receiver accepts either single- or double-stack 30-round mags; the stock is SVD style. Romanian-made BTW.
I aint an expert either, but I did a bit of research before buying one...
The definitions of the SAR models are correct (that's what I got.)
The other variants are made in different countries. Each country has their own name for their AK. For example:
MAK is made in China
MAADI is made in Egypt, etc.
The exception is the WASR, which is also Romanian, like the SAR. WASR's were originally designed to take single-stack magazines only (low capacity, 5-10 rounds). To further confuse things, some have since been converted to take the standard double-stack magazines.
The finished AK's all function pretty much the same. The differences are in the manufacturing processes and the finishes. There are endless debates about which is really better.
Also, there are many good books, including "The AK-47 Story" by Ezell.
Read some of the discussion at ak-47.net, and you'll begin to get a feel for what are considered quality AK's. Milled receivers usually get high marks, for example.