I was hoping for some input... I am thinking of selling a early generation Steyr AUG A3 NATO and I wondered if the quality of the new ones are as good as the early ones if I ever decide to get this rifle again down the road. Does any one own BOTH or has some experience with both generations and know if there are any real differences in quality in old vs new? Any help would be greatly appreciated...

You cannot get a A3 anymore.
Now it is the A3M1 (I think that’s what they are called now)

Different top rail mount and some other less noticeable things.

That’s pretty much it. The M1 is more versatile from a factory option perspective (top rails and optic housings). The A3 is going to have a CL barrel and M1s could be nitride instead.