Hello,
Now I'm following one more friend and now I started to learn PLT Scheme(using DrScheme), but I and my friends normally help each other in some projects, to do this we use revision controllers(normally SVN, in sometimes we use git), but which is the best revision control to use with PLT Scheme? Thanks.
There are two kind of revision control: centralized (svn, cvs) and distributed (mercurial, git, bazaar). If you are familiar with both git and svn, you know about this.
Which one is preferred ? mercurial and git provides the same global features, differences are only in the detail.
Which one should you choose ? The one you are most familiar with.
Really, it's a question of which revision control system works best for you and your workflow. The version control system and programming language are pretty much completely independent, so it doesn't really matter what language you're using as long as the version control system suits your needs. I've used both SVN and Git extensively with PLT Scheme, C++, Ruby, Perl, and shell-scripts, and they both work fine with all of those languages.
I personally prefer Git, but some people find SVN simpler to use, and some people like Mercuiral, Bazaar, or Darcs.
As already pointed out, the choice for a version control system is independent of your programming language. That said, if you would like recommendations, I find Mercurial (Hg) a very nice and easy to use Distributed Version Control system. And you may want to use http://bitbucket.org, which provides free Mercurial hosting.
DISCLAIMER: I have no association with BitBucket, except for being a free user.
As an aside, its a really good practice to maintain your code in a revision control system. It saves against accidental loss or modifications to code.