If you are asking what would be the most effective technique. I couldn't really say without actually performing research on it. Obviously both the ball of the foot and heel would still provide more deformation than the shin, as both are very fleshy surfaces. Both would also probably be safer surfaces than the instep. The ball of the foot would allow for the transfer of energy down the metatarsals (long bones in the foot), just like with a punch, allowing for less damage to any one area or tissue. The heel would strike with the calcaneus which is a very strong bone, and energy could be safely transfered into the tibea. However, both techniques would be more difficult to pull off, which may actually detract from the amount of power the kick could generate.
I think the thing that should be realized is that both kicking with the instep, and the shin can provide enough power for ko's or damage to the torso, and that has been proven time and time again in kickboxing and MMA. Whether one style of kicking is truly more powerful than the other would require fairly indepth research (far more than in that video).
Edit: I do kyokushin myself, but I also have to imagine that MT guys strike the surface with their instep as well. Otherwise they woudl really have to reach
I think the thing that should be realized is that both kicking with the instep, and the shin can provide enough power for ko's or damage to the torso, and that has been proven time and time again in kickboxing and MMA. Whether one style of kicking is truly more powerful than the other would require fairly indepth research (far more than in that video).
Edit: I do kyokushin myself, but I also have to imagine that MT guys strike the surface with their instep as well. Otherwise they woudl really have to reach