Dick size

Hey guys and girls, ive been curious about what dick sizes women actually prefer. Of course, weve all heard the "you are big enough", but how can we be sure? I bought my gf a dildo, that is over 2 inches bigger than me, and loves it. Id love to find her a bull with the ideal size for him, but im not quite sure what it is.
I know not all women are the same, but what are your / your wifes favorite dick size?