S3 if you're already in the AWS ecosystem. R2 if egress costs are killing you.

I run multi-region on AWS and S3 is deeply integrated with everything - IAM, CloudFront, ECS, Lambda. Switching to R2 would save on egress but I'd lose the tight integration with the rest of my stack. That tradeoff isn't worth it unless bandwidth is a significant line item.

R2's zero egress pricing is genuinely compelling for anything serving large files publicly - media, assets, user uploads. If your use case is "store stuff and serve it to users," R2 wins on cost. If your use case is "store stuff and process it with other AWS services," S3 wins on friction.