GitLab has a fine interface and offers free private repositories. If it weren't for GitHub's network effect advantage, I'd use it for all my git projects.
Really love that they have free private repos though.
I also make heavy use of GitHub's issues/milestones system, even on private repos, to keep myself organized. I'd probably use GitLab a lot more if I knew of an easy way to port issues and milestones over to GitHub when I decide to make a project public.
On a related note, can anyone recommend some good external issue tracking systems that integrates well with both GitLab and GitHub?