Ranked in these QuestionsQuestion Ranking
Pro Free for up to 5 users
You can use BitBucket for free if you have 5 or less users (or try it out for free). Price brackets are for 10, 25, 50, 100, or unlimited users (it costs $1 per user per month, or $200 for unlimited users).
Pro Supports both Mercurial and Git
Has full support for both Mercurial and Git VCS.
Pro Native application for both Mac and Windows
Atlassian, the company behind BitBucket is also behind SourceTree, a free application for Windows and Mac wich works as a client for both Git and Mercurial which can be connected to BitBucket and other code hosting services.
Con Integration with other tools is not as good as github
Most of the 3rd party tools ( bug trackers, CI servers, chat servers, etc) always integrate with GitHub first, and either don't integrate with Bitbucket at all or do sub par job in it. For example there are 3 separate projects to allow building and verifying pull request submissions on Jenkins CI server and there is only one viable one for BitBucket and that one is really buggy and lacking many features.
The only exception to this rule is Atlassian products like Jira.