It's too bad this is git only for now. Is there any plan to add support for mercurial repositories?
At this point, the only thing keeping me on BitBucket instead of GitLab is Mercurial support.
Have used both, they are so close, seems "odd" to go for the way less popular one, barring you have a really old HG repo and haven't bothered to switch.
Mercurial has a number of features that git never implemented - in particular revsets. I also prefer the hg CLI over the git CLI. Mercurial has sane, concise online help, and a lot of work went into the design of the command-line to be consistent, composable, and made of pieces that do one thing and do it well.
But, I'll grant its not worth fighting over if I am working with collaborators who have a git preference.