I used both, and in my experience gitea/gogs starts out much faster than gitlab, but becomes slower and slower as repository sizes increase. At some point it became practically unusable, despite the repository not being particularly large.

On top of that we had constant issues with pull requests causing internal server errors, the merge check failing in mysterious ways, and so on. These issues may have been fixed now. We ended up switching to GitLab, and while it's quite resource intensive, performance seemed much more consistent.

Their docker image also goes up blazing fast compared to gitlab.

Also, they have repo mirroring which as I understand is not available on gitlabs CE edition.

Repository mirroring from several sources has been available in GitLab CE for several versions.

One-time, one-way mirroring has. Continuous push-for-push mirroring is still an EE feature.