Quick take
GitHub Copilot is the easiest fit when your code already lives on GitHub and your team wants AI inside the normal developer workflow. It helps with completions, chat, pull request review, and cloud agent tasks. It is strongest when paired with the review habits you already use. It is weaker when a team expects it to replace architecture decisions, security review, or ownership.
Best fit
Use GitHub Copilot for code suggestions, test writing, code explanation, pull request help, repository questions, and small implementation tasks. It is especially useful for teams that already use GitHub issues, pull requests, Actions, and code review.