If you're implying that you're stuck with git if you use GitHub, you can use SVN with GitHub if you really want to.
https://github.com/blog/1178-collaborating-on-github-with-su...
How is that remotely relevant? Mercurial is a great DVCS with a user experience that is (in my opinion) far superior to git. SVN on the other hand is...I don't think I need to rehash this tired old DVCS vs SVN argument.
I would love hg support on github, but until that time will use bitbucket for my own projects, perhaps occasionally syncing to GitHub using hg-git.
Your point wasn't obvious from what you wrote; there's a mention of which DVCS BitBucket supports but not which DVCS you use.
> [BitBucket] has almost all the same features, supports git and mercurial and unlimited private repos.
BTW, GitHub indirectly supports Mercurial. They wrote an hg-git plugin [1] that allows you to push to and pull from a git remote repo using hg.