Formulate your own opinions about which is better for you and your work environment. Personally I and many others prefer git - it certainly works well for GitHub: https://github.com/
But there will always be those who prefer other VCS because of some such reason that is relevant to them. Maybe it will be relevant to you too ;)
What do you mean by 'git and svn clients'? There is already an official client for each of both git and subversion, called 'git' and 'subversion', respectively.
It's TortoiseSVN, and they have clients for git and mercurial as well. I wouldn't recommend subversion these days. It was good compared to CVS but git and mercurial are much faster.
One good graphic client for GIT that I have found and use daily is SourceTree which is free.
It is great for beginners just getting the hang of pushing/pulling, commits, adds, branching, ect. and also have some nice advance features for more advanced users.
It was made by the one of the original creators of Orge3D Steve Streeting and it works with Mercurial and Git.
I would definitely recommend checking it out. http://www.sourcetreeapp.com/
There's also SeeGit: https://github.com/Haacked/SeeGit
It updates in realtime based on the state of your repo - great for seeing the effects of command line interaction.
Neither of them are really that hard to learn. Just take a hour or two to get familiar with one and you should be fine. It is not like learning a programming language or anything.
That said subversion is dying rapidly and wouldn't be a good idea to start using it in my opinion. I would go with Git or Mercurial which provide a better version of Source Control then subversion does and are going strong and won't be gone anytime soon.
Edit: Here is a post that I think describes why not to use subversion pretty nicely http://www.altdevblogaday.com/2011/03/09/its-time-to-stop-using-subversion/ (Though a warning this article is a couple years old and most of the con's against Git have been fixed)
But ultimately the choice is up to you. Choose what you feel most comfortable with but do some research first.
No it doesn't there are plenty of GUI applications out there that can handle that for you like the ones listed so far or even github provides a windows and mac version of one. Here is a nice list of some http://git-scm.com/downloads/guis