Honestly, I don't see why you would have them both on at the same time. But IF you do, I would imagine the SPORTS mode will get the better half. The reason I say this is because you are physically moving the shifter over. That is telling the ECU to shift later. Now it is quite probable that if you aren't getting on it......the ECO will still do some good on the MPGs. I haven't tried doing this so I am not 100% certain on the answer.