Open Source CMS: what's hot and what's not?
To find out what's hot and what's not, they used a number of services and sources to compare the popularity of 19 systems. So it's not a comparison on functionality but rather on market share. Wordpress, Joomla and Drupal were labeled as 'market leaders' in the survey.
The method I found especially clever was 'Twitter Prominence' in order to find out which system people were talking about. Surprisingly only three of the systems appeared in the results: Wordpress, Drupal and Joomla. Wordpress was clearly the winner - with a clear spike at the release of a new version. Drupal also has clear measurable activity but Joomla almost wasn't mentioned at all in the 30-day measurement using Twist.