Redmine offers support for a lot of different versioning systems, we won't force you to use a special type, if you like to use our DevZone to host your project. If you don't have a favorite system, use Mercurial, it is our favorite.
Currently supported by Redmine are:
We have our own SVN server and already installed support for Mercurial, Bazaar and Git, but there is no experience with the last two. (Bazaar & Git)