The M70AB2 is better but both are from Century. Make sure you can examine either weapon before handing over money. You definitely want to look at the rivets, mag wobble, and cant. I'm not an underfolder fan (cheek weld sucks, even with 440/550 wrapped). If you don't have any AKs and determined to get one, find a standard fixed stock AK.
I remember M70s were around $800 (at ClassicFirearms) before the madness and the WASR quite a bit less. Most of the standard AKs are around $900-1k now but no way I'd pay anything near that price.
I have WASR's and Yugo's along with Chinese, Bulgarian, and an IO based on the Polish AK.
The Yugo's, (Serbian) are built on a 1.5mm receiver, where the WASR is built on a 1mm receiver.
The Yugo's are, IMO, built better from the ground up.
On the down side the Yugo's are noticeably heavier.
I haven't noticed any difference in reliability between the two.
I guess your choice should be made based on whether you want a stronger better built, more expensive Yugo, or a cheaper basic WASR.
Both are fine for their intended purpose.
Get the Yugo, thicker reciever ( same used on the RPK), 1.5mm vs 1mm for the wasr.
Now that said you will enjoy better cheek weld on the wasr vs the M70AB2, but there is a cool factor to the underfolder that you will never have with the wasr.
Have owned and shot both. Still have the M70. They are virtually bombproof, easy to work on, and can be made very compact. The cheek weld with cord wrap is OK for me, and at least as good as the WASR fixed stock. Just make sure you get the AB2, not the AB2T, which has a thinner receiver and rivet retention problems. Not as much aftermarket as for the WASR, but some real advantages, such as ability (depending on sights) to take tritium inserts. Just keep the barrel clean (no chrome).
AFAIK none of the current Yugo's have chromed bores, but otherwise they are likely to be superior to the WASR. Sight cant is possible on either but from what I have seen and heard is less prominent on Yugos. WASRs can have mag well issues as they are typically single stacks converted to double by CAI drunk monkeys.