The correct choice is AWS Trusted Advisor. It provides cost optimization checks that surface unattached EBS volumes and volumes with consistently low activity across Regions so you can remove or resize them to reduce spend.

AWS Trusted Advisor runs best practice checks and returns actionable findings that point to orphaned or underutilized block storage. Those cost optimization checks are designed to highlight unattached volumes and persistently idle volumes so you can address them quickly across your accounts.

AWS Config records configuration history and inventory and helps with compliance and change tracking, but it does not natively perform utilization analysis or automatically list idle or unattached EBS volumes for cost optimization.

Amazon CloudWatch collects metrics logs and alarms and can show EBS performance and activity, however it does not perform an account wide assessment that automatically flags orphaned or barely used volumes.

AWS Compute Optimizer provides rightsizing recommendations for instances and volume performance tuning for attached storage, but it focuses on sizing attached resources and does not identify unattached volumes the way Trusted Advisor does.

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