Drupal or Joomla - A Comparison
Drupal Better for Extensibility and Large Sites
Once you get down to slightly less biased issues, it gets more interesting.
Drupal users rate their CMS higher than Joomla users rated theirs in areas such as documentation (especially core and module documentation) and bugs (core and modules). Drupal users apparently feel that their add-ons integrate better with the core, and their framework makes it easier to extend their CMS's capabilities.
Why can't we be friends? Joomla versus Drupal
Overall, I find that Joomla is an excellent CMS for basic to complex websites. The blogging feature is not highly developed, nor is the capacity to multi-purpose your content in different areas of the site due to the rigid filing structure it requires. It has a large user base where the websites seem to be more personal, small business, and non-community-building sites. This last point isn't a cut against Joomla, but only serves to show that it's mostly being used as a CMS and not for building a participative website.
Joomla and Drupal; which one is right for you?
Drupal 11/21 | Joomla 11/21
Drupal is flexible and developer-friendly. It also benefits from a coherent and stable community led by several large and reputable companies.
Joomla 1.6 will focus on improving two crucial areas: Joomla's inflexible systems for managing users and content. It may become a little more complicated as a result, but it will remain relatively easy to produce a good-looking site with plenty of functionality using Joomla.