In terms of technology, I would put it at Natal > WMP > Sony motion.
Why? Because the WMP and WiiMote itself can control object movements, 1:1 motion, and pretty much everything besides that basic video overlay the PS Eye did. The Sony motion doesn't have any way to move your character outside of where your physical body can move. Even using two just allows two "hands" to be used and doesn't allow any character movement like the Wii nunchuck.
Also, both WMP and Sony motion only track one or 2 points, always at the hands. Natal can track multiple points on multiple bodies, and can ignore background motion so waving your hand while your friend is playing won't affect it. It suffers the same problem that Sony motion does, in that the character can only move as much as your body in 3D space, but the overall tracking, voice recognition, and facial/expression recognition is insane.
The algorithms and hardware/software combo being built into Natal is top notch.