At least as far as I can tell, Gitlab seems to be used a lot more than the other two. I don't think I've ever gone to a page for a SourceForge project that was created after maybe 2012 or so, and although it's possible I've looked at a project on Codeberg or Forgejo, I can't think of a single one off the top of my head. Meanwhile, I've run into projects on Gitlab (either gitlab.com itself or a self-hosted version) at multiple employers and various Linux codebases and packages (Plasma and Gnome desktop environments and other various windowing-related software, Arch Linux package sources, etc.).

I guess it's possible that my experience is wildly different than others, but if we're talking about volume of usage today rather than individual preferences, it's kind of shocking for me that someone wouldn't think to reference Gitlab at all in the list of potential successors, let alone not mention it literally first.

Gitlab's interface makes me want to cry every time I have to use it. I would not recommend it to someone who misses classic GitHub. Codeberg/Forgejo/Gitea would be a much better match.