This also brings up the question..which brand of gas is better? Do you find that different brands are better than others? So far from my findings I get the best fuel mileage if I stick with Shell Regular. Chevron/Texaco second. If I go with any other brand, my gas mileage seems to go down a little.
I also bought the Focus so I didn't have to burn mid grade or premium gas. My previous car (2002 Jetta) ran sluggish if it burned regular.