I gender-bend. Stay with me while I try to explore my reasons for doing so.
I'm a heterosexual male and I play almost exclusively females. In fact, I even use female handles out of game.
Let's take a look at my list of reasons, probably in this order:
1. Females look prettier.
2. Males usually look buff, crude, inflexible, and there are hardly genderless alternatives.
3. It's projection stuff. It's what I lack as a personality and what I look for to enhance within myself. I don't need emphasizing what I already have if I deem it would lead to lesser balance. Recognize and incorporate; it gives me a chance to find out about different aspects of me.
4. It may make interaction (trade?) with other people easier due to reason number one. If I choose a buff male avatar, the odds are I might be a 1337 teenage wtf dude dealing with my insecurities as a male.
Strange. I thought I'd have more reasons.
More sub-reasons may be closeted under reason number three.