they're both fairly stiff skis, punx a little softer...
i rode walls as my first park ski in 160cm (im 5'9) and i loved them. symmetrical is boss for skiing switch as well, i ski switch about 50% of the time now, even on groomers etc. thats probably the biggest difference between the two... and maybe if you ski switch a lot then the walls will be a better choice.
however, you cant go wrong with either skis. and to be honest, i havent ever seen a pro ride walls, whereas punx do get ridden by pros... i just dont think volkl has a great park team or something!