Tomas is right, I have found a small number of AGA demos that aren't quite right. For the most part however, it's spot-on. (Many demos and games aren't totally smooth on real amigas, either.) The sound quality is as good or better, but much of it really comes down to your hardware, and how well the emulator is configured for the given task. Many (but not all) instances of poor/choppy graphics performance are due to some setting that needs to be tweaked.
Personally, I prefer WinUAE in almost every way, and have no desire to fire-up the originals (though I keep my 500 and 1200 for nostalgic/collector purposes). It's super-fast, easily customized, you can flick back and forth instantly between Windows and AOS, and it runs about 95% of the things I've tried flawlessly. It's nice to fire up a little Jet Pilot at full detail and framerate (perfectly smooth), on a screen that doesn't make my eyes bleed...something no real amiga could ever manage.
Is it 100% perfect?? No...but IMO, setup correctly on decent hardware, the advantages far outweigh the negatives.
