It all depends on what you want to do.

Wordpress is a straight ahead blog, it's easy to set up and does blogging well. With various plugins you can modify it to do almost anything you want it to do, as long as it's blogging.

Typo3 is powerful if you can get it set up right, which is a major pain in the ass.

Drupal is quite powerful as well, and the one that I use most often. It does lots of things, and it even does some of them well. Its biggest strength is also its biggest weakness; there are lots of user submitted modules. Those user submitted modules give you lots of options for adding capabilities, but they are also of unknown quality.

I haven't used joomla or mambo, though I plan to give them a try at some point.

Joomla and Mambo are nice systems but with a high learning curve. In comparison using wordpress is very easy. Depends on what you need really...imo, most sites with a full CMS could be run with wordpress + addons more easily.

~shiva