It's strange seeing those three content management systems mentioned together like that. Joomla split off from Mambo a few years ago. Since then Joomla is the one to go for out of those two. Nuke (PHP Nuke) is an older CMS that is rather crappy in comparison to other ones out there nowadays. Drupal is a CMS that is a worthy competitor of Joomla, but Joomla is way better.
My vote would have to be
Joomla!
