Joomla! Best PHP Open Source Content Management System…
Don't take my word on it, this is the what the Packt Publishing Award judges say:
http://www.packtpub.com/article/joomla-wins-best-php-open-source-content-management-system
Joomla Wins Best PHP Cms
But it is nice to see “Once again, judges commented on the size and responsiveness of the community, which translates to potential problems being dealt with quickly.”
