Too bad GitHub was out of the question just because it's not open source. I don't think there is a single platform out there that has done more for the open source community than GitHub. Most of the great OSS projects are on it and it helped democratize open source participation by providing a very nice UI and a set of robust tools that simply didn't exist before.
Sourceforge went the way it did not only because it was always a hornet's nest of ads and viruses, but they allowed bloatware and viruses to be bundled with project downloads. I don't see GitHub ever behaving in that way, though if they did there'd be a mass exodus for sure.
GitLab too, but granted, if you host your own version, you wouldn't lose anything.
That being said, GitHub has almost no choice to keep being a good guy with the OSS community. If they lose it, they lose the respect of the developers, and they would lose their paid customers in the process.
Another point for Gitlab is that it can be forked if the parent company goes bad (e.g libreoffice and oracle). When looking at it with this perspective, widely-used essential projects can live and thrive from one party to the next.
GNOME is a free software project (as self-described[0]) not merely an "open source" project. Therefore, while GitHub's place in the "open source" ecosystem and its contributions to said ecosystem are well known (and worthy of respect), it does not share in the principles of the free software community. GNOME, as a free software project (and a subproject of GNU at least nominally[1]), is inclined to select an option in line with its principles.
GitLab is a great first choice. I’ve been using it for 6+ years, heavily in the last 2, and it’s feature set is fantastic. Now I’m getting into the Auto DevOps features and it’s been a great experience.
