I distinguish between 1) the spinning reverse kick I occassionally throw out in sparring but wouldn't use on the street, 2) the back kick, which I don't spar with but WOULD gladly use on the street if attacked from the rear, and 3) the scoop kick, which is a side/back kick hybrid and the technique I'd use in either situation. Mark, you are correct when you say it generates the most force. It incorporates the largest muscles of the body, and the heel is a sturdy striking surface.