For the technicle who have heard of the big three and want to reassure themselves they are useing the right CMS, then this is a good read.

By Brian Proffitt (COMPUTERWORLD) tests three of the top free site-building applications from the Developers point of view. September 14, 2011

Computerworld - Building a website has never been easier. Gone -- mostly -- are the days of having to hand-code HTML and PHP scripts in order to get a slick, fully functional website, thanks to the capabilities of content management systems that do most or all of the heavy lifting for site creators.

There are boatloads of content management systems (CMSs) for serious site creators, but the most common for websites today are three open-source tools: Joomla, Drupal and WordPress. Actually, to call them "tools" is an understatement -- these are full-fledged platforms, with tens of thousands of add-on tools created by very active developer communities.
These applications have a lot of similarities. For example, all three are written in the PHP programming language, all three are licensed under the free GNU General Public License (GPL), and all three depend on the MySQL database to hold and manage the actual content within a website.

Conclusions of the big three.

Oddly, when searching for help on some Drupal issues, I was often pointed at sites other than the main Drupal site. This is too bad, because there are some good docs in there.

A majority of Drupal modules are categorized as non-commercial, meaning free, something which is different from the Joomla extension family. Free software users will be comfortable with this, but commercial users may need to get used to the lack of commercial support.

Documentation on the Joomla site is wiki-based, updated constantly and well-indexed by search engines. So I ran into it a lot more often when searching for help.

There are far more commercial extensions in Joomla, though not so many you get the idea that "free" Joomla is just a kind of come-on for pay-for-more add-ons. The balance between free and paid extensions is fair, and you get the sense that there's a lot more revenue in the developer ecosystem in Joomla. Take from that what you will.

I found the WordPress community to be heavily centralized on that main site, which made it easy to locate tools and support for my questions. I sort of liked the one-stop shopping aspect of this community, and found no problems in finding the answers I need when questions arose.

This is, for me, a clear draw. If you can't find help on the main sites for WordPress, Drupal and Joomla, then you will almost always find the knowledge you need on a third-party site. These are strong communities that definitely add to the strength column of each CMS.

If I were to make a recommendation, I would tell a beginner to use WordPress, no question. The themes and plug-ins are diverse and numerous, and this is a very good starter CMS that can scale quite well into a more complex site.

I would recommend Joomla for sites that are a bit more complex and are going to be managed by someone with stronger technical skills. For this type of situation, Joomla is perfect: plenty of extensions, easier to learn and enough templates to make site design worries moot.

If I were building a much more complex site, though, I might turn to Drupal first. Though it's harder to learn, it has much more flexibility to scale a site in terms of complexity. It also has the ability to scale up into very complex sites to be used for a variety of business needs.

Each CMS platform has a very strong developer community, however, and if you are planning to pay for help in building a site, there are plenty of experts out there to build as complicated a site as you need with any of these applications.