Amazon S3 Glacier Flexible Retrieval (formerly known as S3 Glacier) is well-suited for infrequently accessed data with retrieval times varying from a few minutes to several hours, offering a balance between retrieval speed and cost. Amazon S3 Standard is designed for frequently accessed data, so it would be more expensive for this use case. Amazon EBS is designed to provide block storage to Amazon EC2 instances and is not optimized for infrequently accessed data. Amazon FSx for Lustre is a high-performance file system optimized for fast processing of workloads and isn't cost-optimal for long-term storage of infrequently accessed assets. Thus, the best fit for the given requirements is Amazon S3 Glacier Flexible Retrieval.