I can't say that I'm bothered with Gitlab's interface, even though I've had much more experience with Github. It uses more colors which sometimes has the effect of making actionable clicks stand out better. Commenting on committed code is one such example, for some reason that UI feels more clear to me. Also, on github I sometimes find myself looking for the commit list, which I always find immediately on Gitlab. IMO if you're used to both UIs it's either a wash or slightly in favour of Gitlab - my issues are purely in the backend.