Amazon Timestream is a fast, scalable, and serverless time series database service for IoT and operational applications that makes it easy to store and analyze trillions of events per day at 1/10th the cost of relational databases. It is specifically designed for time series data, making it the most cost-effective choice for the described scenario. Amazon DynamoDB, while capable of handling time series data, is not specialized for such workloads and could be less cost-effective at scale for time-series analytics. Amazon RDS is a relational database service better suited for transactional data, not optimized for time series analytics. Amazon Redshift is a columnar database optimized for complex queries on structured data, but it is not specifically designed for time series data and can be more expensive for this type of workload.