It really doesn't matter which ONE you use. Just use the same one all the time. If your bow arm is straight and your anchor is always in the same place, your draw length will be constant. It's the consistency that you're looking for. If you can, video yourself using the different bows and see what you're doing "wrong" with one of them, then correct it. Note that measuring to the back of the bow with different riser styles can give you a different measurement, even if your form/anchor is perfect. The measurements may vary in that situation, but your draw lenght is constant.