Which AWS service will host this database with the LEAST amount of operational overhead?

Explanations:

Amazon RDS (Relational Database Service) is designed to simplify the setup, operation, and scaling of relational databases in the cloud. It supports MariaDB and provides automated backups, patching, monitoring, and scaling, resulting in the least operational overhead.

Amazon Neptune is a graph database service. It is optimized for graph applications and does not support relational databases like MariaDB. Thus, it is not suitable for hosting the MariaDB database.

Amazon S3 (Simple Storage Service) is an object storage service, not a database service. While it can store data, it does not provide the capabilities needed to host a relational database such as MariaDB, making it unsuitable for this use case.

Amazon DynamoDB is a NoSQL database service that is designed for key-value and document data models. It is not compatible with relational databases like MariaDB and would not be suitable for hosting this type of database.