you also might want to take a look at
http://www.cmsmatrix.org/ -- its hosted by the people at plainblack, so, webgui gets a little boost in that it supports 'everything'.
but, its a good place to look around to see alternatives.
Then, whichever you choose, search for cmsname bugtraq in google to see how many security exploits they have, and the response time of the team involved.