I already did this move yesterday. I was using GitLab just for private repos, max 2 devs each. Was an easy move for me.
As a platform, I am more a GitHub fan user. Like it or not, the community is all there, this is my de facto public portfolio, makes all sense for me.
I still use BitBucket most for projects hosted by my clients, so, for this I don't have the power of choice. But all my projects are already on GitHub, and as market move, was good, but I don't think it is a breaking change for GitLab. The GitLab's CI still rocks in a lot of ways, and they still have the power of not being powered by Microsoft, something a lot of people are trying to avoid.