Here is a node describing my experiences with several varied CMS systems.

I think that it really depends on what you want from the CMS. If you simply want something to publish articles/pages then there are many to chose from. If you need strong and quick customizability then you may want to look at the Nuke-like systems (Xoops, Drupal). If you need strong workflow controls look for the more capable systems (Plone/Zope, Bricolage). If you need ease of use look for the wysiswyg systems (Mambo, Callisto).

Check out OpenSourceCMS for lots of ready to try out installations of these systems.