First did it in Kotor because the female PC had much more fun conversation choices with Bastilla(namely she'd be a catty bitch towards you and it was hilarious.)
Then in Elder Scrolls Oblivion because if you wanted to look good, all of the best looking clothing and armor was for CBBE body.
Mass Effect 1-3 because the female PC had better lines and better inflection on the sarcastic lines.
World of Warcraft as a blood elf because when I tried it for shits n giggles I made 25 gold in the first hour of play from people just throwing gold and items at me for no reason.