While in most cases, better quality parts are in separates. A lot of electronics are crammed into avr's and usually when al that stuff is crammed into one box, the audio quality will suffer, but some will not notice. @ channel separates are made and designed with one goal in mind, and that is to sound good. As mentioned before, it's an old debate. Kind of like, do all amps sound the same. And it probably boils down to preference and how good of an ear you have. None of it or anyone elses opinion should affect your decision. Let your ears be the judge.
All that being said, my preference is separates.