For me the best one is CMS Made Simple. I love this CMS because it is really simple to understand for editors without special knowledge. Easy to setup for webmaster. And is extremely friendly for designers. This CMS is pretty "old" and even without having any marketing it managed to win a packt award and shared the second place with Joomla. Unfortunately there are still not enough tutorials that can show how easy it really is. Therefore I write tutorials myself in English and German and have opened a website in Russian also to support it.
We moved almost all of our blogging clients from wordpress to serendipity and dropped our support tickets for them by 60%. Most of our clients are on paired Serendipity/Gallery installs. I myself started on PHPNuke and still host a number of them. I'm on Movable Type myself.