so I got asked a question about getting gas from two different gas stations, where brand a got 4 more miles to the gallon then brand b did but brand b costs less. I don't know the question so here is is and I'm hopping one of you will have an answer.

Is the gas that the car is getting a higher mpg on easier on the engine in terms of will it take longer to wear out any of the parts than using the other kind of gas? given that we aren't going to drive the car any differently either way and it is a fairly modem engine (2008) 
and neither gas station is out of the way so we aren't putting any extra miles to get the gas, and both gases are advertised as having the same octane rating.

is it just down to something as simple as we might have to change a filter more often or could have bigger effects?