Having traveled almost as much as Hub (and others) I've found individual places (usually small dives) that make great pizzas. My absolute favorite is in San Jose Costa Rica. Just a few tables - huge (ugly) wood fired oven on the patio and when they run out of dough they are closed. Never, ever had a better pizza.
But, Hub is right - without New York and Chicago (that's my order) at the top of the list, it just doesn't make sense. These are our pizza cities.