Spot instances are good for short term requirements as they can be very economical.
Sometimes AWS may terminate your instance, e.g. when the market price exceeds your bid
price. This is a good option for non-critical workloads that can be terminated
On-Demand is not the most economical option
Reserved instances are good for long-term, static requirements as you must lock-in for 1 or
3 years in return for a decent discount
Dedicated hosts provide a full server dedicated to a single customer and is therefore
expensive