Interesting. Actually we initially moved from Bitbucket's tracker to Bugzilla because at that time Bitbucket's tracker was pretty limited.
Today, there is JIRA which seems to be full featured and well integrated with Bitbucket. More importantly, it turns out that we are more and more often discussing patches through pull-requests as Bitbucket is much more convenient than Bugzilla for such a task. Discussions are thus split between Bitbucket and Bugzilla which is not very nice. So I guess this is an option we should seriously consider for the near future. What do others think?
To help everyone make a decision, I'll try an import on a clone.
gael