The answer to that question is actually pretty involved. Reverse Cowboy (the man faces her feet) rates high for ass access (spanking high for the womans comfort/ lack of pegging skills, high for the womans visuals and high for prostate stimulation (he rides it how it feels best).
Some men say its the girth that gets them off, others say its the length and position of the dildo. 18)Does the man have to be submissive? One is to have a bullet vibe in the base of the dildo (in which case you need to make sure that the harness you use is open in the back so the base sits against her lady bits).