Generally Subversion .. However you should watch out for resource issues.
When I was working for a game company we had a few directories containing hundreds of tiny files, and other directories that contained a few hundred meg files. When we swapped from CVS to Subversion, the speed of checking out the repo decreased from one hour to four or five hours. Updating was also substantially slowr.
This is almost certainly due to using either http or ssh to transmit file data, compared to the native csv pserver, however since it is so easy to setup svn over ssh or webdav people tend not to think about the protocol overhead. You can however use a native svn protocol and this should alleviate the issue, we did not test this at my old company.
Another issue that is often ignored is storage space, we found that subversion did use several times as much storage locally as CVS. I seem to recall that it stores a local copy of the repo data to speed up diffing, this won't be a huge issue unless you store several gigabytes in your repository.
