From a StackShare Community member: "We’re debating going with Amazon RDS for PostgreSQL or Amazon DynamoDB. Cost is our main concern but we’re also curious about other potential benefits/differences. Which one would you recommend and why?"
I use Amazon DynamoDB because it integrates seamlessly with other AWS SaaS solutions and if cost is the primary concern early on, then this will be a better choice when compared to AWS RDS or any other solution that requires the creation of a HA cluster of IaaS components that will cost money just for being there, the costs not being influenced primarily by usage.
Amazon RDS for PostgreSQL or Amazon DynamoDB? If you need to follow RDBS concepts choose Amazon RDS (PostgreSQL). This choice will guarantee a stable relational database with a great support for years from PostgreSQL Global Development Group. But, you need a great scalable NoSQL database. You can use Amazon DynamoDB. The most important thing about this is that you can use RESTful HTTP API to access data.