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Ethanol free fuel provides the most BTUs (energy content).  That means the best power output and fuel efficiency.  However, ethanol has a higher octane rating than 93 octane gasoline, so it provides improved resistance to knock/detonation.  That additional resistance to knock can be critical when running a tune, as the actual gasoline octane rating can vary by source.  Sticking to Top Tier fuel is a good way to ensure you're getting the octane you're paying for.