Female breasts are an eternal mystery to men.
Why are they so attractive to us, anyway?
I think it's something that happens on a molecular level.
However, if guys seem to favor one over the other, I think it's because of being right-handed or left-handed.
To a right-handed man, the left breast on a woman is more easily accessible.
. . . I always try to give them both equal attention, but I always seem to start with the left one.