GitHub Actions is the default for open source and most small teams — free for public repos, generous tier for private. The hosted runners are slow but acceptable.
For larger orgs, self-hosted runners or paid alternatives (CircleCI, BuildKite, GitLab) typically beat GitHub Actions on speed by 2–4× for the same workload.
The right question: does CI duration block your deploy cadence? If yes, invest. If no, save the money.