Comparing cloud storage

Cloud Datastore is the best for semi-structured application data that is used in app engines applications.

Bigtable is best for analytical data with heavy read-write events like AdTech, Financial or IoT data.

Cloud Storage is best for structured and unstructured, binary or object data like images, large media files, and backups.

Cloud SQL is best for web frameworks and in existing applications like storing user credentials and customer orders.

Cloud Spanner is best for large scale database applications that are larger than two terabytes, for example, for financial trading and e-commerce use cases.