I have not worked with Joomla, but I suspec there are similarities between Drupal and Joomla.
I was drawn to Drupal because of the Content construction Kit: I wanted to have more possibilities than just one title field and a content field with tinymce and leave it to the user how the content is styled (as is the case with a lot of CMS's out there). But what I realized is that Drupal is very complicated. It is not so that I am afraid to learn something that is complicated, but I was simply asking myself if all those complications are worth it/ are really necessary.
- Drupal can be used for BIG websites, with a large editor staff and a professional workflow. Think websites for IBM or Sony, think websites running on their own iron inside the corporate headquarter.
- The backend is complicated - although you can dumb down the backend by controling what user can view what items. And if the normal install does not give you enough tools for that, you can download various modules that will give you more options. But the backend will remain complicated nonetheless
- Drupal is complicated to theme, but because it is complicated it gives you all sorts of control of various minute details- you have to know how to work with those details inside the Drupal universe. But in many cases you are trying to find tricks to change the output of other functions with your own functions in order to get the result you need. I am not sure what this does to the overhead of the site, but it does not feel good.
- There are zillions of modules out there that help you change various aspects of a site. But the thing is that it looks like a lot of those themes change output from other functions with their own functions. Again the overhead question.
- One of the ideas behind drupal is that a coder/themer can develop a theme in such a way that even someone without coding/theming knowledge can change the look and feel of the site from the backend (not just the colors of a site but also modules like 'Views'). This gives additional complications in the back-end and extra overhead.
In the end I realized that I did not need nor want that kind of complications, not for me and not for my users. My websites are not that big, and I thought it is more important to have a system that:
- offers me freedom to style a website easily and quickly (development speed)
- at the same time offering me various options to expand functionality + add extra fields that offer me extra control over the design (I am the designer, so I am payed to control all aspects of a design, when I am offering the user a CMS to edit the content of a website)
- offers my users a backend that is easy to work with (again: I am the designer, I also have to pay attention to the way my users can work with the content for their own website)
- and if you need that professional workflow, my guess is you can develop it
And for me that would be silverstripe, but I must confess that I am not working that long with it...