im going to be bold here and tell you that eclipse has better sound quality. My Eclipse 3434 sounded better than my pioneer premier 880 in my opinion. The eclipse is just so dam transparent and it sounds good out of the box. With Pioneer, you have to do all this fine tuning on the eq's and hpf's lpf's to make it sound good. And I haven't got that all done yet. The only reason I got the pioneer is because it plays cd's while its mounted face up in my tuffy center console in my jeep. Eclipse decks cannot do this well. Many times I couldn't play cd's because the mechanism couldn't handle being at that angle. This pissed me off. So unless you are mounting it face up in a jeep security console, get an eclipse!
oh and on a side note, the only thing that pioneer does better than eclipse is the mp3 capability. My 880 reads stuff super fast and easily, while my eclipse 3434 took days to access mp3's and sometimes it would put tracks way out of order. In some cases it would act like the songs weren't on the cd because it couldn't read them. Pioneer does all this right.
I still have that sad feeling in my stomach because I feel like I'm not getting that some eclipse sound quality!