I'm coming to this discussion a few years late, but I'll pitch in some thoughts from the procurement side for prosperity. The landscape changes, but for commercial CMS, I'd look at the vendors recommended by research firms. For open source solutions, I'd look for a large active community, documentation, and a support model you could live with.
We started research for a CMS in 2008 with online searches and the ultimate CMS list http://www.cmsmatrix.org/. (boggles the mind how many "CMS's" are out there)
We ended up looking at ".NET-friendly" CMS recommended by Gartner and Forrester. Gartner's "Magic Quadrant" of leaders/challengers and niche/visionaries and Forrester's "Wave" point out both feature sets as well as marketplace and vendor roadmap.
A good request for proposal (RFP) or comparison tip isn't to ask "do you feature X?" but to compare and see which solution does it better.
At the time, Kentico and Sitefinity were on our evaluation list as .NET-friendly. We also considered DotNetNuke, though there was a mild objection to "becoming DNN programmers" rather than staying mainly .NET (I'm sure there's a mis-perception in there, no offense).
We ended up comparing RedDot and Tridion and found Tridion to be a better fit for us because of its .NET API and flexibility.