I always found that iTunes sounded worse to me than winamp, and people shot me down saying "they can't possibly, check the sound enhancer's not on!"
To this day, I still maintain that winamp sounds better.
Just to clarify though, I'm not necessarily talking about things sounding more.. Eh, how do I put it... Well think of the difference between monitors and a nice set of hi-fi speakers. Monitors go for ultra clarity and transparancy, hi-fi speakers are made to sound nice, which may not be a perfect reflection on the source material.
I have compared Winamp to Reaper and I find they sound quite different to my ears, too, but compared to winamp vs itunes, I will not say either sounds "better," just different.