CMS: The Big Three

A quick review of web content management systems suggests that there are three free systems that have substantially more market share than others.  We may want to think if it would be appropriate for us to limit our consideration to these three systems: WordPress, Drupal and Joomla.  A very recent comparison with some graphical statistics is at:
   http://www.networkworld.com/community/blog/drupal-joomla-wordpress-smackdown

A PDF which compares the 'top' 20 open CMS systems is available at:
   http://www.waterandstone.com/sites/default/files/2010%20OSCMS%20Report.pdf

There are plenty of other CMS systems out there, including just the free ones.  However unless we have some strong advocate for a particular system, I don't see any other natural dividing line and my inclination would be to start with these to see if one of them can meet our requirements.  Sarah's listed many of the requirements in here previous post (I think a choice of mayo or mustard on the sandwich is needed too) but we'll want to delineate these more completely and clearly and see how these tools match up.

I did a bit of searching on how difficult it is to copy web sites from one of these systems to another.  Generally it seems to be non-trivial but not a horrible task so there is some ability to transition.

The overall impression I get in reading many discussions of these is:

Similarities:

All have a free core system but significatn use of any of these typically involves getting plugins that address specific needs.  Some of these plugins may be commercial, but are typically not very expensive.

Differences:

WordPress, Joomla and Drupal go from easiest/least powerful to hardest/most powerful.  However new releases in all of these systems are reducing the differences on all sides.  WordPress has moved from being primarily a blogging platform to a full-featured CMS.  Drupal is providing more out of the box capability to users.


If there are members of the team that can comment from experience on comparisons of these systems that would be very helpful.  Since these are evolving rapidly mentioning when you used them would be helpful.