Drupal is incredible powerful all round system, it has been developed to be modular and easy to adapt to almost any situation, it is used by large organisations such as the onion for delivering articles, but can just as easily be used to create web2.0 based applications. Underneath the front end of the system is an expandable system allowing programmers and module developers to hook into the core system without having to recode any vital files. However Drupal has a sharp learning curve and would perhaps not be suitable to webmasters or bloggers who just want to get it up and running as quickly as possible.
Wordpress is one of the most popular CMS available and it gained its popularity for a reason - it's a great CMS (and it's free)! While some aspects are not perfect such as SEO, they can surely be improved by a plugin developed by their huge user base.
Joomla is an excellent CMS system that enables those with very little developing experience to create their own sites. The system works out of the box, but we advise for you to add some more functions to make your Joomla site more robust and functional. Note that a buggy extension can break your website, so test everything before you decide to use it.
