Both types of hurdle stretches loosen up the hamstring in the same way. But the hurdle stretch with the leg pointed back puts sideways torque on the back knee and can result in injury. So while the potential benefit of the exercises are the same, one risks serious injury to the knee.
Probably would be something high-level for a long period of time, and the recommended period of time to exercise is 60 minutes a day, so i would chose C
