Subversion is currently the leading version control system worldwide. It is much more advanced and powerful than the old Microsoft Visual SourceSafe system. It is also free and open source, widely supported, well maintained and has an excellent range of free clients that you can choose from.
If you are choosing a version control system specifically for Help+Manual, the choose SVN. Team Foundation Server (TFS) is much more difficult to configure and maintain and significantly less flexible. There is really no comparison – for use with Help+Manual SVN is far superior to TFS.
Microsoft has now discontinued Visual SourceSafe, so you can no longer get it if you don't already have it. Even if you do already have it, we recommend switching to Subversion (SVN) unless you have a special reason for staying with VSS.