Just go with whatever the manufacturer recommends. They always have actual data to back up their recommendation. Its not like they have a stake in the gas companies. If that was the case then every manufacturer would only recommend premium.
Actually, ethanol is a cheap way of raising the octane level of gasoline.I would just use premium. Not because people say you get better mileage. Not because people say it makes it run faster. But mainly because most premium gases don't have ethanol mixed in.