I voted only male, but sometimes I pick to female like in Fire Emblem to make harem runs challanges (only one guy+all other units female, or one girl+all other units males). Those games all feature some classes that are genderlocked, which is an additional incentive to change avatar gender sometimes
I'd say I play male 95% of times when given option. Since in almost all games the difference is merely cosmetic, I prefer to play guys. Sometimes though I really enjoy the female character models so I pick them