You can use both the routes however Kallar Kahar - Katas - Choa Sedan Shah - Khewra route is more picturesque. You will have to climb and then descend mountains of salt range after Choa Sedan Shah so make sure your vehicle's brakes are good.
Use motorway M2 to reach Kallar Kahar, as I have mentioned earlier, the Chakwal route is in pretty bad condition.