Rear or Front - There is little difference in performance. What is best for you will depend on the application. If you are allowing pinion angle change with a spring or rubber in the top link or lift bar then the panhard location will be more important. Front mounting will cause the rear roll center to raise when you accelerate which will help the car turn. A rear mounted bar will drop the roll center making it easier to get traction. A front mounted bar can be lowered more but in some applications interferes with components. When a rear panhard is used with a quick change it requires either a longer axle mount to clear the gear cover with a straight panhard bar or a short mount with a hoop style bar.