I do use and like Gitea and it is indeed dead simple to deploy. On the other hand, it doesn't provide any continuous integration / delivery out of the box. You could roll your own by hooking into the Gitea API but at that point you are at a level of effort that exceeds that of deploying a GitLab instance.
Feature-wise, GitLab is also much more convenient for managing big, complex projects.
On the other hand, if mostly all you need is a Git repository viewer + bug tracker + wiki, Gitea does a perfectly good job with very low effort.
As for GitHub, I think the only thing it's got going for it is a critical mass of users who already have accounts in it, but that makes it more of a "social media" than a developer site. If you are a big open source project that for some reason needs lots of people hammering your issue tracker, then it might do the job, otherwise you're almost certainly better off with one of the other forges.
Horses for courses, etc.