I play at M/M. For as others have said, diplomacy is better (especially those important trade agreements), the rate at which the AI attacks me seems managable with armie, navies, finances, etc., and I don't like bonuses given to the AI. Also, as before mentioned, I don't want the battlefield AI to have any bonuses either! All in all, I've had several entertaining campaings playing vanilla at the M/M difficulty level.