Despite it being "less advanced", like Phanx I find GIT annoying to work with. At least in a workplace enviroment here. Have always preferred SVN.
One Windows option for GIT that hasn't been mentioned yet that I currently use:
Git Extensions. 100% free/GPL open source, been around for quite a while, is regularly updated and works from Windows Explorer like TortoiseSVN does. Find it a lot more convenient to use than, say, msysgit. And looks to be more stable than TortoiseGIT (though I haven't tested that).
For SVN, the #1 Windows choice is as others have mentioned:
TortoiseSVN (also 100% free/GPL open source).