Well... nice topic that is going to turn into flame wars.
I used all three, and also DLE, PHP-Nuke, SLAED, 2z, etc.
Each CMS has its own niche it fits best. Wordpress is excellent for blogs; Joomla is cool for non-programmers; Drupal is nice for sophisticated developers. Each one can be (mis)used almost everywhere. All require some tweaking and toying before using in production environment.
Myself, I prefer Drupal. It has the most clean and well-structured codebase, is very flexible, supports different theming engines, has tons of modules and great community.
However, I would not recommend Drupal for a really high traffic dynamic website. Actually, no one of the mentioned CMSs can handle high load well. By "high traffic" I mean 30+
logged in users actively working with website
at the same time, when website is hosted on a standard shared host. Anonymous (non-logged in) users are not a problem most of the time.
Joomla is not as flexible as Drupal, especially when it comes to custom content management, though its capabilities are enough in most situations. The newer branch of Joomla, released earlier this year, still lacks many useful modules which are being ported slowly, so it's better to go with the older branch if your needs are beyond basic install.
Wordpress is... well, everybody knows it. The latest 2.5.x branch is cool. Haven't had time to explore all the changes in it yet. This is the best blogging platform available for free now.
(shameless ad) If you would ever need an advice on Drupal/Wordpress performance and scalability, or need someone to build a site, just
drop me a PM. (/shameless ad)
Good luck!
Wish your sites bring you profit no matter what CMS you choose.