Study published in British Journal of Urology (BJU Int.) 2009 Apr; 103(8):1096-103. Epub 2009 Feb 24. The study used a self-reported questionaire and reports on various genital and nongenital areas in terms of erotic sensitivity for intact men (uncircumcised).

Abstract
OBJECTIVE:
 
To assess the perceptions of healthy men of their genital anatomy and sexual sensitivity, along with the re-test reliability of these ratings, in a new self-reported questionnaire, the Self-Assessment of Genital Anatomy and Sexual Function .

RESULTS:
 
There was little variability in anatomy ratings. Ratings of overall penile sensitivity to sexual stimulation gave higher values of 'sexual pleasure' for penile stimulation by the partner than by self (P = 0.002) and marginally higher ratings of 'orgasm intensity' by partner stimulation (P = 0.077), but there were no corresponding differences on ratings of 'effort needed to reach orgasm' or of 'discomfort/pain'. Overall discrimination between genital areas was highly significant (mixed-model anova, P = 0.001) for ratings of 'sexual pleasure', 'orgasm intensity' and 'orgasm effort', but was not significant for 'discomfort/pain'. Ranked by degree of 'sexual pleasure', the area 'underside of the glans' was highest, followed by 'underside of the penile shaft', 'upper side of the glans', 'left and right sides of the glans', 'one or both sides of the penis', 'upper side of the penile shaft', 'foreskin' (11 subjects), 'skin between the scrotum and anus', 'back side of the scrotum', 'front side of the scrotum', and 'around anus', but not all pair differences were significant. The rank order was similar for 'orgasm intensity', but less similar and with fewer significant pair differences for 'orgasm effort'. Overall discrimination of other body parts that help orgasm when touched/stimulated was also highly significant (P = 0.001) and included (in order of degree) scrotum, ear, skin between scrotum and anus, neck, breast/nipples, buttocks, anus (exterior skin), anus (inside with penetration), wrist, and axilla, but many pair differences were not significant.