Have a look to the following data from this year 2012 about CMS market share:
WordPress
Easily the most accessible and possibly the most commonly used, the strength of WordPress is in its quick installation and the massive user and developer community that results in a vast array of plugins and enhancements for the platform.
Throw in the added bonus of a vast template library and easy PHP and CSS file editing from within the admin screen and it becomes quite clear why WordPress is used for everything from personal blogs to e-commerce websites.
Joomla
A quick trip to the Joomla website will reveal the claim that millions of websites are running on the software, and the reason for this is simple – it is extremely customizable, suitable for pretty much any purpose.
This is why Joomla is often used by small and medium businesses, large organizations, non-profits and individuals. Joomla’s admin section is easy to use and with the vast array of options from templates and styles to adding feeds, content blocks, menu management tools and more, you can see why this is a popular choice.
Drupal
A popular free and open source CMS, Drupal is often one of the first choices when building a new website. Like many of the other tools listed here, Drupal can be scaled for personal blogs or enterprise mega-sites, and like WordPress there are thousands of modules that can be added to increase functionality.
