Female,
Most games that allow the distinction eventually give bonuses for going against the opposing sex, and since most baddies are guys it just makes since.
If I'm not receiving some sort of gender biased reward, I know it's only polygons but; I'd rather stare at the fiction back side of a pretty lady for 70+ hours than that of a man.
Fallout New Vegas is the first game I've seen that let's the ladies get a perk to hit on other ladies, and guys hit on guys, so I might actually do a play through as both. Especially once wasteland prostitution and nudity gets remade for this new post apocalyptic setting.