Spot Fleet and CloudOptimo both provide diversification across many Spot markets by supporting multiple instance types. Spot Fleet does not provide diversification over a percentage of On-Demand as a guaranteed safety net. Every instance will always be a spot instance of some kind. If your application’s availability requirements can tolerate that level of risk, Spot Fleet is a good choice. If giving up a few percentage points of cost savings for an On-Demand safety net sounds appealing, then CloudOptimo would be a better choice. A second difference is that Spot Fleet does not natively integrate with the AutoScalingGroup constructs widely used in many existing deployments. It does have an AutoScaling capability recently launched, but it must be set up and managed separately, and requires making code changes to the application to get new instances to register with an existing AutoScalingGroup and/or ELB. If you have an existing stack using AutoScalingGroup, you can leverage CloudOptimo immediately, Spot Fleet will require some development work. In addition, CloudOptimo provides additional cost-saving features that Spot Fleet does not, such as constantly rebalancing instances as prices fluctuate. The end result is CloudOptimo typically manages clusters at a lower price point than Spot Fleet does.