I'm everyone's been asked this question at least once. But seeing as how most engines made in the past decade are engineered to take both even though a lot of them recommend using only premium. So whats your 2 cents about about this topic?
Just go with whatever the manufacturer recommends. They always have actual data to back up their recommendation. Its not like they have a stake in the gas companies. If that was the case then every manufacturer would only recommend premium.
I would just use premium. Not because people say you get better mileage. Not because people say it makes it run faster. But mainly because most premium gases don't have ethanol mixed in. Also premium gases can remain stable in your tank way longer than regular gas. Meaning if ever for some reason you're unable to start it up for a long time it wont gunk up the fuel lines.
If you purchase a car with the R20 it wouldn't really matter.. it will be better for the long run, so might as well settle with sliver gas 89 or something.