[JSC]

According to this report there is an difference in gas.

...

but the question is which Brands are better

I just received this card from Audi (Canada) listing the sources of "top Tier" gas that Audi is recommending. I don't recognize many of them, but assume this list covers North America, but I am not sure.

 

[JSC]

In my market area BP is the best. Why? They do not put ethanol in their fuel.

All Top Tier rated fuels are required to be minimum 10% ethanol. Ethanol produces worse mileage and power than 100% gasoline on an engine designed for 100% gasoline.

If you are using a boosted engine then the tuning can be modified to take advantage of the extra detonation control that ethanol has over gasoline. Otherwise it is not beneficial.

FWIW, I get about 1mpg better when I fill with BP over Shell, QT, Conoco, or Chevron. All are available in my local area.

I think you mean maximum 10%. The top tier spec is 8-10% ethanol.