I prefer female, but that is personal choice lol.. F/f f/f f/F etc is my cup of tea. Others here are F/m M/f etc.... Having multiple options means more folks play it, and having both spanker and spankee options same thing. The easiest way is to make it one sex, one choice of spanker or spankee, but that cuts down on number of folks that will truly enjoy the game. Then again, it is your game, so you have to take it where YOU want it to go.
For example, if I EVER get time to work on my game again, it will be an F/f, f/f game exclusively, with rather severe spankings. Yes I know it will cut a LOT of players out, but that's what I focus on.