Over the debate between Amazon RDS and Amazon DynamoDB i will go for Amazon DynamoDB because i tried using Amazon RDS for handling our database for our mobile app VirtualRobe but on each query request the cost was just getting ridiculously high and our monthly AWS bill increased. Therefore we decided to try out non-relational database Amazon DynamoDB, it was quite cheaper but lead to us handling lots of database relationship and functionality such has linking a user table to clothes he or she wore last by doing all this load in the backend when it could have been a child table to the user table on Amazon DynamoDB In all when it comes to cost, i go for Amazon DynamoDB but when it comes to the best database to use with more query flexibilities for apps that requires complex queries i go for Amazon RDS.