To accommodate both predictable baseline usage and intermittent spikes, the best approach is to combine Reserved Instances (RIs) for the baseline capacity with On-Demand Instances to handle peak loads. RIs offer a discounted hourly rate and capacity reservation, making them suitable for the steady baseline workload, while On-Demand Instances provide the flexibility to scale up without any upfront commitment, which is ideal for handling unpredictable spikes. Savings Plans require a commitment to a specific amount of usage (measured in $/hour) over 1 or 3 years and could lead to overcommitment during non-peak times. Meanwhile, Spot Instances offer the highest discounts but can be terminated by AWS when the spot price exceeds the bid price, which risks stability during demand spikes.