Some background on these:

Gitea is a fork of Gogs. Both are written in Go and are pretty light on resources (they support SQLite as database backend).

Gitlab is heavier on resources and requires at least Postgresql and Redis.

Gitlab looks nicer and has a lot more features even in the open source edition. (Though some paid features seem to be arbitrary paid vs free, like scoped tags, a feature everyone could use is paid, while a really Enterprise feature like kubernetes support is free)