I believe in Joomla.
Maybe because before using it I read a book on it which was kind of motivational at some point (something that even so you have a gut feeling that it may be bias, you still fall for it).
Never the less, I checked it out on my own and like the potential Joomla provides, it is powerful and I love that.
Also I do like WordPress.
I guess it all depends on what you are looking for/what you need; sometimes less sophisticated CMS (which I would say about WordPress) can be great and be a whole world and in other cases it might be a little island in the ocean, so you will need something that won’t be as light, but will provide more (here I would say Joomla). I find both of them convenient... they are popular for a reason I guess.
Another good one that I had a feel of is MODx. That I had recently found through one of my clients who needed some design updates. Personally I liked it, well and not only me… according to my client, managers of his company and some partners overseas who had to make minor updates on regular bases told that it is very easy and they loved it.
If I had to choose one, I would choose Joomla; which I am doing soon for one of my websites. I just like a lot of potential and directions to go in.