The correct answer is to route the logs to a single region Cloud Storage bucket with the archive storage class, as it is the most cost-effective option for long-term storage. Other options are less optimal: updating the retention policy on the _Default log bucket does not address cost-effectiveness; BigQuery is suited for analytics rather than long-term storage; and a multi-region standard storage class bucket is more expensive than a single-region archive storage class bucket. For more details, refer to: Routing and storage Storage classes.