Spot Instances are the best option for the client's needs because they offer a cost-effective solution for workloads that are flexible in their running time and can tolerate interruptions. Spot Instances allow users to take advantage of unused EC2 capacity at a discount of up to 90% off On-Demand prices. Reserved Instances are not suitable for such infrequent and short-term use. On-Demand Instances don't provide the same level of cost savings as Spot Instances for interruptible workloads. Savings Plans require a commitment to use a specific amount of computing power over a one or three-year period, which does not align with the client's occasional workload. Dedicated Hosts would be an unnecessary expense given the intermittent nature and tolerance for interruption in the client's workload.