On-Demand Instances are the most suitable option for the given scenario because they allow users to pay for compute capacity by the hour or second, depending on the instances chosen, with no long-term commitments or upfront fees. This gives the flexibility to increase or decrease compute capacity based on the demands of the application and is an excellent choice for the startup, which is still in its initial uncertain stages. Reserved Instances would not be ideal as they require a longer-term commitment. Savings Plans require a commitment to a consistent usage amount. Spot Instances might be interrupted and are not suitable for the steady-state workload described. Dedicated Hosts and Dedicated Instances are for specialized use cases that require dedicated physical hardware and come with additional costs.