Female lead characters in video games tend to be more dynamic, sophisticated, interesting... just generally better characters. This is because game designers, as a rule, have to work harder to justify a female lead, with male characters it is an "of course they are awesome because they are big and tough guys".
As such I generally prefer female video game personas and almost always play as a female character.
Whether it is a girl playing or a guy playing I never extend assumptions of gender past the avatar, and never invite conversations into real life scenarios. So unless you make it a point to tell me you are a boy or a girl, I'm going to attach the gender to your screen name of that of your avatar (which a lot of people don't, I remember one guy screaming about at me about how he wasn't gay, he stopped when I pointed out that his avatar was a female and that neither one of us actually knew the others gender)
He of course assumed I was a guy until I said that, then he assumed I was a girl... he never did ask, it was kind of funny. If anyone ever asks me if I'm a guy or a girl online (and I will point out that I have never once been asked my real life gender by a female "avatar") I generally ask "why?" before I answer the question. I mean, does it really matter?
I suppose if you are cyber-sexing it up... but that's never been an issue with me.