Bitbucket → Competitors
Plan projects, collaborate on code, test and deploy.
When to use Bitbucket
Is great if you are looking to have private repos without any additional costs.
When to use Github
If you can afford the monthly plan for private repos, Github should be your default choice (given the huge community & large number of open-source projects).
When to use Mercurial
Irrespective of the project size, Mercurial's decentralized development model can be used by users who are less experienced than pro-developers. This is because unlike other CVS, Mercurial doesn't allow its users to change history.