Which AWS service will store this data MOST cost-effectively?

Explanations:

Amazon Aurora is a managed relational database service that provides high availability and durability. While it is suitable for structured data and complex queries, it is generally more expensive than other storage options for storing large volumes of log data.

Amazon Elastic File System (EFS) provides scalable file storage for use with AWS Cloud services and on-premises resources. It is designed for use cases that require file-level access and is typically more costly for storing vast amounts of unstructured data like server logs compared to other options.

Amazon Elastic Block Store (EBS) provides block storage for use with Amazon EC2 instances. While it is good for data that requires low-latency access, it is not optimized for cost-effective storage of large datasets like server logs, especially when considering backup and scaling costs.

Amazon S3 is an object storage service that offers scalability, data availability, security, and performance at a low cost. It is ideal for storing large volumes of unstructured data such as server logs due to its pay-as-you-go pricing model and durability features, making it the most cost-effective option among the choices provided.