Good article though I would disagree about AWS Reserved Instances. Though they are way more complicated, they can give 40%+ discount and in many use cases you can run quite a lot of them.
Isn't it true that those require a 1-yr or 3-yr commitment? You can't move a reserved instance to another region. IIRC, its tied both to a region and AZ.
OTOH, spot instances can be cheaper but then you should be prepared for those to vanish anytime.
As of September 2016, you can buy a convertible reservation that allows you to move a reserved instance to a different AZ within a region. Your greater point still stands but I just wanted to correct one piece of it.
