Card carrying RPG transexual here.
I prefer to play as female characters mainly because I think female character design has so much more attention to detail to it (note I don't really play non-human RPGs, no particular reason, I just don't play that many RPGs). Compare the armour sets in Guild Wars for each of the classes for example, or even the dancing?
I think that when it comes to character design female characters aren't signed off on until every detail is just right, whereas with the male characters its just a case of "Yeah, that looks OK at a glance so it it'll do, what's next?"
With an RPG I can expect to spend a lot of hours staring at what the character is doing. A stupid looking beard? Prestige armour that takes ALOT of effort to get but will look rubbish for my character?
Sod that. Dude looks like a lady it is.