The Storage Admin role is the correct choice because it provides the necessary permissions to create and manage Cloud Storage buckets and files, adhering to the principle of least privilege. This role ensures your colleagues can perform their required tasks without granting excessive permissions. The Project Editor role is too broad, granting unnecessary access across all GCP services. The Storage Object Admin and Storage Object Creator roles are insufficient as they do not provide permissions to manage buckets or, in the case of the Creator role, to manage existing objects. For more details, refer to Google Cloud's IAM roles documentation.