Reserved Instances and Savings Plans are the most cost-effective purchasing options for a compute workload that is steady, predictable, and uninterruptible. Reserved Instances provide a significant discount compared to On-Demand Instances, and Savings Plans offer flexible and consistent savings on EC2 usage. Both options require a commitment to a consistent amount of usage, in USD per hour, for a term of 1 or 3 years. On-Demand Instances are suitable for short-term, irregular, or unpredictable workloads, but they are more expensive than Reserved Instances or Savings Plans. Spot Instances are the cheapest option, but they are not suitable for uninterruptible workloads, as they can be reclaimed by AWS at any time. Dedicated Hosts and Dedicated Instances are designed for compliance and licensing requirements, not for cost optimization. They are more expensive than the other options, as they run on single-tenant hardware. References: Instance purchasing options, Amazon EC2 Pricing, 4 Ways to Purchase Amazon EC2 Instances