The most cost-effective option for workloads that can be interrupted is using Spot Instances. Spot Instances allow customers to purchase unused EC2 capacity at a discounted price, which can offer significant savings compared to On-Demand pricing. However, these instances can be terminated by AWS with very little notice if the capacity is needed elsewhere, which is why they are suitable for jobs that can tolerate interruptions. Reserved Instances are typically used for long-term, steady-state usage, and On-Demand Instances are used for short-term, irregular workloads that cannot be interrupted. Savings Plans offer cost savings but require a commitment to a specific usage amount over a 1 or 3-year period, which may not be suitable for the irregular nature of batch processing jobs.