What is your favorite Content Management System?

Drupal (http://www.drupal.org)! It is open-source and the development community is very strong in both numbers and enthusiasm. I've made a wide range of websites using Drupal as a base: newspaper websites, blogs, social networking, photo sharing. Its probably the most easiest open source CMS to develop for and comes with some good APIs (that are well documented) http://api.drupal.org .

A few websites currently using Drupal (note this is just a few of the top of my head:
http://www.theonion.com (newspaper)
http://www.observer.com (newspaper)
http://www.recovery.gov (Obama)
http://www.mtv.co.uk/ (music)
http://www.popsci.com (magazine)
http://www.leadel.net/ (Interesting flash social site)
http://www.mylifetime.com/

Magento, WordPress, Magento are the best content management system. These CMSs are easy to use and understand. Herehttp://ultimatesoftwarereview.blogspot.com/2015/01/top-5-content-management-systems-of-2014.html you can see the list of top content management systems with their brief description.

Depends on what type of a website I need to achieve. If it's a simple personal hub (ie. blog and gallery) or portfolio website, then I like to go with Wordpress. It's simpler. But if I need to build a community site that needs room for expansion, then I'd like to go with Joomla or Drupal - more scalable - just add the module(s) needed.