The purpose of the backswing is to put the club in a position to hit the ball squarely and with authority. The best backswing position for you is the one that lets you come down into the ball freely and without any hitches.
In order to find the position that fits your physique and flexibility, try this exercise.
Take your stance over a ball and:
1. Lift your arms until your upper arms are next to your ears. The clubshaft should be pointing away from you. Stay in your address posture, i.e., do not stand up straight in addition.
2. Without moving your hands, point the clubshaft straight up in the air by bending your wrists toward your head.
3. Turn your hips to the right until they come to a comfortable stop. Let your trunk and arms keep turning to the right as far as they will comfortably go.
That's it. You're there. Three steps to a backswing position that fits you.
Perform the exercise at a consistent rhythm. If you have a ticking clock handy, one move per second is a good pace. There's no need to rush or slur the steps together.
After you have practiced this a bit, as soon as you get into that final position, go right into your downswing and hit through the ball. You might find this to be a freer and more balanced swing than the one you have now.
Keep doing this exercise until the position has fixed itself in your mind. Now you have a target to hit when you start back from the ball -- you know the place at which your body needs to arrive.
It will never hurt to go through the exercise a few times every day just to remind yourself where you are headed when you take the club away from the ball.