The basic diff is that in Drupal you create the Content/Block type for the specific app that you build.
Drupal is heavier than Joomla, more detailed, and has an expanded WordPress logic.
Joomla is easier compared with Drupal, you can learn it faster than Drupal and it uses an MVC programming pattern.
Joomla has fewer Free/Pro Themes and modules than Drupal but is more popular.
Both are more scientific than WordPress, where people from not the WEB area can build sites.