My original avatar was male, but it was going nowhere. This avatar was originally run by my sister and had a much more interesting life - she got NeverDie as a mentor for a start.
After a year or so she gave up the avatar to a friend, and then it ended up being passed to me 2 or so years ago, at which point I had to abandon my original avatar.
So I became a female avatar unintentionally, at the time of giving my own male avatar up to take over this one I was thinking things like "armours cheaper" etc like most others. But the thing is that just isn't true anymore these days, only with the very high-end armour and the only reason there is still a price-gap with those is due to the fact that they are sold so seldom, so the prices still mainly reflect year old prices.
Despite the fact there is no real advantage to the sex of the avatar, I've become fond of her now so I wouldn't swap back.