As for the GitHub for Windows - I have used it for a little time and it's pretty nice. Very esthetic and quite straight forward. It's even better when working with repositories located on GitHub (however I used it with other targets as well).
Today I switched to completely new client for Windows made by Bitbucket named SourceTree. As I understand it's a port from Mac client and thanks to that it looks and feels great. It has LOADS of options and tools (I have not familiarized myself with many of them) and it's constantly developed ( http://blog.bitbucket.org/2013/03/19/introducing-sourcetree-git-client-microsoft-windows/ ). They released the Beta version on 19.03.2013 and they have some really nice plans for future (Mercurial support as well!). I do think that it's worth a look.
