We use the Atlassian stack at my job, and I'm not a fan.
Jira in particular is maybe my most hated software on the planet: yes, it's very powerful, but it also too complex and unintuitive. I remember on the first day using it, I sent them about 5 tickets about various usability issues (buttons are not where you'd expect them, extra clicks needed for basic stuff, etc), I didn't get any replies (i suspect that the feedback button leads to nowhere).
BitBucket is mostly ok, but it's slightly less appealing than Github. For one thing, the ecosystem around Github seems friendlier: integrating Travis for example with Github was a snap, but integrating Jenkins with BitBucket was a nightmare (and also I don't think Bamboo is free for open source). You can tag issues in commits in Github as well, btw. But perhaps the best argument for sticking with Github is visibility: it's the most popular option, most developers are familiar with it and there's an organic stream of new developers interested in the project that I don't think we'll get with Bitbucket.
As for confluence and project management, Github has both a wiki and a project management tool which we can use (the functionality might be more basic, but it's also more friendly, and good enough for our needs, I believe).