Each has a purpose:
WordPress: Blogging
Joomla: CMS Management. Easy to use.
Drupal: CMS Management. Harder to use. Great for developers.
I use Joomla. Screwed around with Drupal once and didn't feel like learning another CMS. Basically, I haven't came across anything that I couldn't implement into Joomla. That may change. But for now: Joomla!
Joomla is better than Wordpress when using social related sites. Wordpress is better when the site isn't focused on users. Joomla is more extensive and you can script it, using it's backend. However, Wordpress is more lightweight and for sole content management, it's plenty good enough.
So, if you need total development control: use Drupal or Joomla
If your site isn't centered around membership: Use Wordpress
If you don't care: pick one.
