Mid grade octane is your best bet, and ethanol added fuels are common around here, but whether they are harmful to an engine is debatable. The cheapest grade burns too quickly, and premium is probably too pricey. I usually run mid grade for three or four fill ups, then run a tank of premium to clear up deposits. Running your engine full out a few times a month also helps keep the carbs clean, to blow out the cobwebs, as the gearheads call it.