Then very recently I've had to use Gitlab for a variety of new projects. And just... wow, it has come a long way.
There is an incredible amount of tooling and features, native to Gitlab. It's actually scary, and in some places even gets messy (feature overload). But a lot of it is useful stuff Github really should be offering. Things like more metadata on projects, subprojects. A very in-depth permission system (invite users with read-only access, issue-only access; membership expiration, ...). Branch protection integrated into various features.
Native CI! That's the big one. Travis is terrible. I used Gitlab CI to deploy one of my most recent project and ... it's been great. Was very simple to configure, felt a lot less magic and constrained than Travis, and it's very well integrated into Gitlab.
All this to say that I'm just about converted. Unfortunately, I have my 10+ year old profile on Github which includes membership to various projects and orgs, but I'm now pretty definitely using both platforms.
Edit: Here's my Github profile so people know I mean business when I'm praising Gitlab. https://github.com/jleclanche