GitHub Enterprise comes with included SAML SSO support, and a huge free tier for Actions and Packages, which gives your team everything they need to get off to a great start and scale up without hitting any roadblocks along the way. An important point to consider is that GitHub Enterprise comes in both self-hosted and cloud-hosted variations, so you don't need to manage your own infrastructure for it unless you would prefer to.

With GitHub Enterprise, you also plug in to the largest development community in the world, and can collaborate directly on the open source projects that are probably already part of your stack. You can also access the latest and greatest in development tools such as GitHub Codespaces, GitHub Co-Pilot, and much much more, with great new features being shipped every day.

I'd lean towards GitHub (either billing plan) for one key reason that is often overlooked (we certainly did!).

If you're planning on creating OSS repositories under your start-up's name/brand, people will naturally expect to find the public repositories on GitHub. Not on GitLab, or Bitbucket, or a self-hosted Gitea, but on GitHub.

Personally, I find it simpler to have all of the repositories (public and private) under one organisation and on one platform, so for this reason, I think that GitHub is the best choice.

On the DevOps side, GitLab is far superior to GitHub (from my experience using both GitHub Enterprise and GitLab Ultimate), but for the one aforementioned, we're using GitHub at Moducate.