I have compared Drupal and Joomla. Essentially, I found Drupal to be the one for me based upon being able to easily create custom content types, having a more flexible approach to membership levels and access rights for users than Joomla and imo being able to quite easily customise various aspects of the templates and modules. There is a learning curve, but there is also quite good support available, people are quite willing to share code / customisations and there are a good range of modules available to help with most requirements and certain aspects of seo. www.teamsugar.com is a nice example of a site using Drupal, although which system you use will very much depend upon what you want it to do.

My 2 cents.