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Well, I've always found both Joomla and Mambo to be very, very similar (in fact, *almost* identical in terms of features + look). Drupal is also nice, but it's not as user-friendly. If you are looking for a CMS that has a cool, user-friendly interface (and easy integration with forum software), both Mambo and Joomla would be good choices. If you are looking for a CMS that is flexible and extremely customizable, Drupal would be a good choice.
There is no comparision to Drupal. See my signature. That is the type of sites you can build using drupal. Its just a matter of getting started in drupal. I agree it may take a little bit more, but once you choose cms like joomla or others which are not as easy to customize then you are stuck
On the other hand if you are good with PHP programming , then it does not matter much which one you choose. since you are going to build your own modules anyway. Joomla has good collection of themes if you are looking for out of box themes.
There are a lot of goods one, just find one you like and learn it well. Most of them are not any better than the others, just different.
I would avoid commercial applications though, getting one fixed if it is broken can be an expensive nightmare. Stick with Open Source.