Top Tier is a description of the quality of detergent additives put in gasoline. A dirty secret in the gas industry is that ALL gasoline, no matter the refinery, is the same and usually mixed. Gasoline is distributed throughout the country through pipeline systems. When Exxon puts 100 gallons of 87 octane gasoline into the pipeline, they get immediate credit to pull 100 gallons of 87 octane from the pipeline. However, chances are the 100 gallons they pull will NOT be the same from any of their refineries, but is most likely from another source, like Conoco Phillips or Citgo. The only difference is the additives that get added at the pipeline depot before the trucks deliver it to the gas station.
As far as using 91 octane, you’ll never see a bump in fuel mileage. The engine in you Malibu and Accord are designed to run on 87 octane. Adding 91 octane will not make any difference except to your wallet. Klick-and-Klack has a great article discussing this issue.
If your looking for Top Tier fuels, look here.
And, chances are, you will not see any mileage improvement with ethanol-free fuel. The 2012 models were designed with ethanol fuels in mind, probably even to the 15% ethanol level proposed by the EPA. And there are some models that even allow for E85 (85% ethanol) with the flex-fuel engine. These cars are already tuned to get the best mileage based on available fuels and the difference in E0 to E10 is not enough to detect. It is definitely not enough to make up a $0.30 to $0.50 per gallon difference.