I have been working with Mezzanine for close to a year and a half now and it has been great. The community is awesome and Steve (and others) are very responsive and helpful on the mailing list. I really like page_processors (http://mezzanine.jupo.org/docs/content-architecture.html#pag...) which allow you to easily add additional functionality on a per slug or per model basis. You can also specify templates on a per slug or per model basis. The simplicity, ease of getting started and ease of modifying Mezzanine push it beyond the competition IMHO. It takes care of plenty of things for you and gets out of your way and lets you develop when you need it to.

Note: I don't actually have much/any experience with Django-CMS so I can't make a fair comparison.