I did what the others recommend: go to best buy (etc) and try both. I bought a zune. I could have gotten a ZVM for $199 or a zune for $249 + free power pack (car charger, etc). I was planning on buying a car charger anyways as i plan to use it for road trips and such.
Zune:
- not a ums device or drag n drop in explorer device
- sounds great
- bigger screen
- slightly bigger i think
- wifi built in (although it currently is useless)
- have to transcode video (but i haven't messed with video, don't really plan to)
- supports mp3 / wma / aac
- software actually isn't as bad as people make it out to be. i sync'd up my (un-DRM'd) mp3 collection fairly quickly and easily. I haven't used it for any of it's music management functions, so maybe that's where the gripe is
- looks better (IMO)
ZVM:
- cheaper
- plays a wide variety of video formats
- more open. i think it's a standard windows multimedia device which may be drag n drop but i'm not sure
- sounds good
- works on linux
oh, and the mother of all comparison charts:
http://www.dapreview.net/zune_vs_ipod_vs_zvm.html
I choose the zune hoping that future upgrades to the firmware will make the wifi useful. And i'm crossing my fingers hoping that rockbox will one day work on it.