Like I said before: The ZVM's sound quality is a teeeeny bit muffled compared to the Zune's. Well, I'm the kind of guy for warm, clear sound... And the Zune's SQ is very, very clear compared to the ZVM's. I can hear almost everything in the song: Vocals, strings, different percussions, etc. Then again, it might be because of the stock songs the ZVM features and the Zune stock songs. I did a custom EQ with the ZVM though and got almost the same SQ as the Zune... So you could go either way.
The ZVM has superior video quality compared to the Zune... Plus it supports more video formats. I mean, the Zune converts everything to LQ WMVs... Which was annoying as hell because I put an HQ movie on my Zune and it turned out muddy. This could also be because of the Zune's bigger screen. Same pixels with both players=Bigger pixels with bigger screen=Muddy screen. Plus, the ZVM has a brighter, more colorful screen.
So in short:
The Zune's SQ:ZVM SQ as to TV:Widescreen HDTV.
And vice versa with video quality.
My two cents go with the ZVM though.
~JJ