This study, recently published in the Journal of Sexual Medicine, has been reported on widely, despite it being small and not originally intended as a examination of penis traits generally considered most attractive. The researchers were interested in the impact of surgery for hypospadias, a congenital condition characterized by a urethral opening in the wrong location (i.e., not at the tip of the glans), on perceived penis attractiveness. Because they had subjects rate control penises (i.e., those unaffected by hypospadias), they also had data demonstrating aspects considered most attractive for penises in general.
From Refinery29:
For a new study published in the The Journal of Sexual Medicine, the researchers asked 105 women in three different age groups — 16 to 20, 25 to 30, and 40 to 45 years old — to rank the importance of "eight penile aspects," including girth and length but also such traits as scrotum appearance. According to the women, the most important aspect was "general cosmetic appearance," followed by pubic hair appearance, penile skin, penile girth, glans shape, penile length, scrotum appearance, and position and shape of the urethra in last place. One takeaway, then, is that penis owners feeling insecure about creatively positioned urethras can relax.
In addition to ranking penis traits, study participants also compared 10 photos of circumcised penises with 10 photos of penises that had been surgically treated for hypospadias, a condition in which the urethra is located on the underside of the penis; the participants then rated how "normal" they found the treated penises to look (they weren't informed beforehand which penises were which). Apparently, this study was inspired by the shame that some people with hypospadias feel, even after receiving surgery. The women in the study found the majority of the penises with hypospadias to look as "normal" as the circumcised-only penises; the change in their reactions to "different"-looking penises was deemed too small to be relevant.
Read the rest here.