Driving Modes..

Use whatever mode works best for you, different drivers get different results. Those buttons change only the user interface at the gas pedal, not anything within the propulsion system. (Well, except for allowing some more slop in cruise control and air conditioning operation. When you are trying to achieve top mpg, you probably have both of those turned off.)

Those of us who are a bit clumsy, but patient, are most likely to do best in ECO. Better coordinated but less patient drivers may overcompensate for ECO's filtering and delays, and do better in Normal or PWR.

In theory, the very same mpg should be achievable in all three modes. But only drivers lacking common human frailties are likely to see this.

Many drivers don't see enough mpg difference to bother overriding a choice based on preferred touch and feel.