http://www.piratino.ch/
Gets my recommendation. Near Altstetten.
Dominos can also be good but they are expensive and I dont like how they handle (or in fact dont handle) with their mistakes. Until they changed Pepperoni to Salami on their online english menu I kept getting pizzas with something like green peppers and mushrooms. When informed they just said that in CH pepperoni was in fact green pepper and were clearly expecting that this explanation would be the end of it and that I should stop wasting their time. They did not just excuse them selfs and put another pizza with the right toppings according to the online order straight in the oven.
And to top it all, they insisted in getting the wrong pizza back, INTACT!