In vault 68 you have 999 men, but only 1 woman. In vault 69 you have 999 women, but only 1 man.
If you are a woman and picked vault 68 you'll be the only woman. If you are a man and picked vault 69 you'll be the only man.
(BTW I am a Straight man)
If I was Straight I would pick vault 69, regardless of gender (because even being a women I wouldn't want that many men).
If I was I gay man I would pick vault 68.
If I was I gay woman I would pick vault 69.
If you are a woman and picked vault 68 you'll be the only woman. If you are a man and picked vault 69 you'll be the only man.
(BTW I am a Straight man)
If I was Straight I would pick vault 69, regardless of gender (because even being a women I wouldn't want that many men).
If I was I gay man I would pick vault 68.
If I was I gay woman I would pick vault 69.