I have not worked with Joomla or Comentum but have done extensive work with Drupal. That said, there's a reason Drupal has become widely adopted with grassroots

I have not worked with Joomla or Comentum but have done extensive work with Drupal. That said, there's a reason Drupal has become widely adopted with grassroots campaigns. They often have limited technical resources, just lots of eager volunteers. Drupal has a great theme engine with a very active community so you can do quite a bit of look n feel stuff with simple web interface and no PHP work. If your mockup needs to do anything dynamic then Drupal's very extensive framework might be too easy to get lost in.