Sharing ChatGPT's answer with you guys.
To minimize the cost of the backup solution, you should choose the storage account that is located in the same region as the web app. In this case, the web app is located in the West US region, so the best option for the backup target would be storage2 or storage3, which are also located in West US.
However, since storage2 is a BlobStorage account type and storage3 is a BlockBlobStorage account type, you should consider the specific requirements of your backup solution. If your backup needs to store only block blobs, then storage3 would be the more appropriate choice. On the other hand, if your backup requires different types of blobs (page blobs, append blobs, and block blobs), then storage2 might be a better fit.
Therefore, the best option for the backup target would be either storage2 or storage3, depending on the specific requirements of your backup solution.