ZDNet UK reviews five Linux flavors, trying to decide which one is the best for small business (not from home users and enthusiasts point of view).
This is what their comparison comes to:
SUSE Linux 10
Novell Linux Desktop 9
Red Hat Desktop 4
Mandriva Linux 2006
All in all I can agree with their ratings, but still find that SUSE/Novell should be scoring higher than Ubuntu, as their primary focus is for business segment. Also I can note that I, personally, found the reviews not that professional and comprehensive enough.
Here are links to individual reviews: