For my Honda brushcutter, since it's a 4-stroke I run 89 octane ethanol-free (Union 76) with regular Sta-Bil. Only a few stations in my area have it but the nearest station is only 5 miles away. I talked to Honda and they recommended non-ethanol gas whenever possible and also Sta-Bil.
On my 2013 Mustang GT 5.0 liter with 420 hp/390 ft-lbs torque, I run highest octane gas available. Hard to believe the thing has 11:1 compression and will run on any pump gas. And at idle it purrs like an, uh, tiger. Combined MPG? 15.
On my Nissan Versa Note (which is my daily driver), I run the cheapest gas available: 87 octane. Combined MPG? 38.