High octane gasoline actually has a bit less energy than regular gas. For one thing, ethanol is a cheap octane enhancer, and it has a lot less energy than regular gasoline. But ethanol aside, there is a slight difference because it has more branched hydrocarbons in it (premium).
The gas companies like to claim it has more detergent additives, but in reality it rarely does. Costco sells top fuel gasoline which is a good type to use. Borh grade have it.
My car recommends premium, but it runs fine on midgrade, I haven't tried regular in it. Costco doesn't sell a midgrade.