First consider the question in context….of a true Walsh driver…if you understand how they work the waveform must propagate along the driver surface, so a stiff non pistonic cone is ideal.
in a more conventional box speaker / driver arrangement, IF you want the output to look like the input, you want a pistonic driver. IF the speaker / driver designer is focused on recreating the input aka music without distortion, they will have to get creative with various exotic materials like aluminum, bextrene, doping, kevlar, carbon, balsa wood, etc…. None of which constitute a free lunch.
The key here is output = input, otherwise you are buying a tone control you like… nothing wrong with that…. Audiophile know thyself….
Jim