Here is a side-by-side comparison of Joomla and Teamsite: http://kwebdesign.ca/cms/content/view/106/73/
Being as Teamsite's license is proprietary, it's possible that you'd be limited to what you can or can't modify (though I'm guessing here, read their license).
If you're worried about being able to modify the code (for use and/or redistribution) I'd recommend one of the open-source options that have a compatible license (which is most all of them). Actually, I don't see a whole lot on the comparison that would make Teamsite better. The open-source solutions may be a little more work, but they're also a whole lot more flexible. Some of the open-source solutions (e.g. Joomla) have commercial support options. They also have a huge amount of add-on's available -- and they don't cost extra.
When I face a project, I exhaust all available open-source options before debating the paid route. And so far, I haven't had to purchase anything. There is honestly so much good software out there that dedicated, super-talented people put time into, and work as well (if not better) than paid counterparts.
HTH