Personally, I use a Mercurial repositories on my local machine, and then mirror them on both Bitbucket and (via the hggit plugin) Github. Provided they're all kept relatively up to date (and I tend to push after every few commits, but avoid pushing after a commit where the test suite is failing), there is no reason for any of them to be more official than any other. I'll happily accept pull requests through either Bitbucket or Github; they'll be pulled to my local repository and from there to the mirrors.

In your META.yml/META.json file, point not to the repository you think if most "official", but to the one you think will be most useful for potential contributors. This is probably Github simply because of the vast number of programmers who already have logins for it.