The principle of least privilege suggests granting only the permissions necessary to perform a task. For managing files and buckets in Cloud Storage:

• roles/storage.objectCreator allows creating objects but not managing them.
• roles/storage.admin provides full control over Cloud Storage, which is more than needed.
• roles/storage.objectAdmin offers the right balance, allowing management of objects without broader project permissions.
• roles/owner grants full project control, far exceeding the required permissions.

Thus, roles/storage.objectAdmin is the most suitable role for this scenario.