I picked my current one (Subversion) based on the quality of the graphical clients it has.

That's apparently heresy to a lot of people, but RCSs are one aspect of programming where I can't get excited. All I wanted was a nice little client where I can browse the repository and click commit on a folder.

Oh, and it has to be able to rename directories without editing the damned repository!.

For windows, TortoiseSVN is very nice and well integrated, and for Unix, RapidSVN is better than the command line. user administration is separated from the system, which is a nice feature too.