A stronger jawline is the result of a high level of testosterone, testosterone levels are responsible for physical characteristics that resemble good genes to women, (subconsciously) women are attracted to men that will pass on the best genes for her offspring. Personal preferences or not, there is a big chance you will be more attracted to a square jawed man.
Ps. For all the men/boys who are about to go and get testosterone shots after reading this, the jaw (and most other physical attributes affected by testosterone levels) only develop during puberty, so get yourself a time machine while you’re at it.