It’s a matter of opinion and lots of it depends on your preferences.

Github: Where most developers are and therefore has the best network effect. Easy for new contributors. Gitlab: Got some traction after Microsoft bought Github, but is very similar, just not as popular. Codeberg: Completely open source (I believe) it’s the option with most respect for your privacy. Lacks the network effect until fediverse integration is complete, which I do believe the platform is working on. Cgit: A very simple git repository viewer. You can’t do anything from it, except see the repository. Some big projects use this, like the kernel.

There are more options, but some gets very specific after this.