Pay-as-you-go for all workloads to ensure maximum flexibility without any upfront commitment, but may not be the most cost-effective for predictable workloads.

Reserved Instances for the critical application to guarantee high availability and cost savings over time, and Spot Instances for the batch processing job to take advantage of lower costs for interruptible workloads.

Spot Instances for both the critical application and the batch processing job to minimize costs, accepting the risk of interruptions for all workloads, which may not be suitable for the critical application.

Reserved Instances for both the critical application and the batch processing job to ensure cost savings and high availability, disregarding the flexibility to scale down during off-peak times, which may not be efficient for the batch processing job.