Unless the club is twisting in your hands, clubface position at the top is dictated by your grip and wrist conditions (bent, flat, or arched). If you have a strong grip and a flat wrist the clubface will point more skyward. If your grip is weak and your wrist is bent or flat it will appear more open.
Personally, I prefer a neutral grip and a flat wrist at the top where the clubface will match the angle of the wrist at the top. Just remember the more open the face at the top the more you have to work to get it closed... if you struggle with a slice, a wide open clubface at the top is not what you want because you may have to find other ways to close the face like timing the flip.
Also, I'm not sure that I would call clubface conditions at the top of the backswing a fault unless you hook the ball and have a closed face at the top, or slice the ball and have an open face. Even so you have to be careful because grip and wrist conditions are the cause of what you are seeing with the clubface at the top.
You just have to be sure to mix the right elements in a golf swing together. Therefore, assigning a general preference as to what clubface position at the top is preferred wouldn't be possible. A more open clubface at the top my be helpful for one person and disastrous for another. Just make sure that whatever you are doing fits with your pattern.