The Cloud Storage Transfer Service is specifically designed for efficiently transferring large volumes of data, such as terabytes, from other cloud storage services like AWS S3 to Google Cloud Storage. It supports scheduled jobs, making it ideal for one-time transfers. While gsutil cp is a useful command-line tool for Cloud Storage operations, it's not optimized for large-scale data transfers. Cloud Dataflow is intended for data processing rather than storage transfer. The Transfer Appliance requires physical access to the source network, making it less suitable for cloud-to-cloud transfers. For more details, visit Cloud Storage Transfer Service.