I've been running GitLab internally on k8s for 6 years, it handles code, CI, security scans, build artifacts, helm charts, etc. It runs a nightly backup to a GCS bucket.

Monthly upgrades are painless. Once a year the major versions (18 to 19, for example) bump external dependencies and we need about an hour on it.

I've been using GitHub for other projects and for the life of me I can't see a single area where its better. Actions is worse without versioned and self documenting components, there's no concept of a project hierarchy or inherited permissions, even simple things like setting up deploy keys are more annoying than they need to be.

I can't speak for GitLab.com - I've never used it.