Does the handbook specify what Octane is required? ie 95 regular or 97 super?
Personally I try to buy from a busy petrol station, to ensure fresh petrol and from either Shell, Esso, BP or Texaco. I never use supermarket gas. Petrols do deteriorate in the large tanks under fuel stations, so using a busy forecourt is a worthwhile exercise. Shell Optimax used to lose it's octane rating in the tanks very quickly.
For some reason, I don't know if this is psychological, my little Twinny (remapped) seems to spin best on Texaco 95 octane.