The gsutil command-line tool also enables you to transfer data between Cloud Storage and other locations. While you can use gsutil to work with Amazon S3 buckets and transfer data from Amazon S3 to Cloud Storage, Storage Transfer Service is recommended for this use case.
Follow these rules of thumb when deciding whether to use gsutil or Storage Transfer Service:
When transferring data from an on-premises location, use gsutil.
When transferring data from another cloud storage provider, use Storage Transfer Service.
Otherwise, evaluate both tools with respect to your specific scenario.
Use this guidance as a starting point. The specific details of your transfer scenario will also help you determine which tool is more appropriate.