Truth in advertising: I own neither, but both are nice. 
More Truth In Advertising: I will be buying a Zen Micro.

Now that that's outta the way...

You can find lotsa reviews on portable audio here:
http://portableaudio.engadget.com/

Or CNet's portable audio section: http://reviews.cnet.com/Music/2001-6450_7-0.html?tag=cnetfd.dir

I'm sure a few other folks can recommend review sites.

In the end, you gotta get your hands on each unit and try it yourself.