Size. Not length but circumference. In order of decreasing average circumference, white, black, Asian.
Some sources say females derive satisfaction from a fuller feeling, which corresponds to male circumference. But too much is too much? And men do tend to prefer a tighter feeling. One would expect the female size of the equivalent organ to correspond to the males' size.
IF true, this would explain the apparent hookup frequencies discussed above.
(Note these are averages; there are outliers.)
The idea that black men have larger penises is media perpetuated and false.
http://wiki.answers....an_men?#slide=6