The one they have the easiest time with. They're all designed to do the same thing. They differ in their integrations with other services and such...but GitHub is so ubiquitous that most services can integrate with it. Even AWS as I noticed their Amplify service can also build and deploy straight from GitHub and even do preview build/deployments from branches on pull requests in GitHub.

Only other real concern is budget if one was significantly more expensive for some reason. The first concern is simply finding tools the team is comfortable with and finds valuable enough to use. Nothing worse than buying a bunch of services and tooling that go unused. That's just waste and confusion.