Subversion Command Line
After using subversion for the past couple of years I have tried various GUI clients and unfortunately none are as fast and as powerful as the command line.
With the help of shell aliases and simply helper scripts (@matt ex-mt knows all about these) you can get the job done quicker and with a lot less hassle than bothering with a GUI client.
My shortcuts are as follows:
That being said, if what you are doing is simple and you are not that technical in mind like Helen keeping her phd thesis in a repository then I would recommend TortoiseSVN. But it falls over when you start dealing with repositories which have gigabytes of files in them.