From ak-47.net:
SAR' s have six U.S. parts to make them legal to have the pistol grips, and accept double stack mags. WASR's have the Druganov style stocks and all Romanian parts, and have been converted from single stack mags to accepting double stack mags. The SAR's were made to accept DS mags, the WASR's were not and are missing the dimples on the sides of the receiver to help snug the mags in the receiver. From what I have read and heard, the WASR's are just fine though. Either one will be OK.
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So basically, the SAR1 is imported in parts, then assembled with US parts so that it can have a pistol grip. The WASR is imported with a butthole stock, and can only accept 10 round single stack mags. The WASR mag well is then machined here, to accept hi-cap mags, and US parts are added to allow a pistol grip.
The end result is, the SAR was designed to support double stack mags, while the WASR is retrofitted to accept them. I would venture the WASR would be just as good, but you might get one with a sticky/loose magwell, or feeding problems, if the work was done poorly. Probably hit and miss, just like the quality of the early SAR-1's.
I have a 2001 series SAR-1, and it runs like a champ. While many feel these rifles are only worth about $250 - $300.... we will not always be able to find, a reliable, high capacity AK variant, so it's get them while you can. Eventually even the basic AK variant will cost the same as the basic AR..... so $300 is a good deal.