I usually buy both games, keep one to work on my Pokedex, collect Shinies/legendaries/events/etc and the other I'll restart over and over and over, trading rare items(like the master ball and in previous games, TMs) over to my main file(In this case, White). My main files is always a boy and I always pick the fire starter.
However, often times I'll pick a girl for my other file...except this generation. After getting the water starter to trade over and playing as the female trainer, I didn't much care for the way she looked. So, playing through for the grass starter now, I'm sticking with the male trainer and probably will unless my next play through I forget how much I dislike the female sprite. =P