I'd use AWS only if you are intending to have your app auto-scale from the start. Aside from that, it's not worth the extra expense (about twice the cost of a comparable Linode) and hassle (you must manage S3 backups, at the least... or lose everything when a shutdown/failure occurs). Start on shared hosting and if you need more room horizontally, you can always move the app to AWS later, when traffic justifies it.