I agree with everyone that said it depends on the classes. Some classes simply look better male/female, so it's on a case-by-case basis. Most of the time I end up with numerous characters of both genders.
With that being said, i'm really glad that guys are allowed to play girls. I can't imagine how the actual girls would be treated in a game where every immature guy could be 100% sure that the girl is actually a girl. By having a lots of in-game girls being guys IRL, you can only hope that some people actually stop themselves for a moment, to think of that possibility, and thus saves someone the bother. Obviously, that's not always gonna happen, and it doesn't kill the real problem (which is immature guys) but those are always gonna hang around anyways.
Cheers for a free world. Two cheers for a free cyberworld.