What is the best flour to use for pizza dough?
What do we look in a pizza dough?

There are many styles of pizza: Italian Vera Pizza Napoletana, Chicago style, ... All of them have something in common in their dough: it should be stretched without tearing, and shouldn't stretch back.

Also, some recipes call for long fermentation times: 6, 9 or more hours at room temperature. With this you get a more relaxed dough (it won't stretch back), and more flavour.

Which flour characteristics give us that dough?

Millers use a tool called Alveograph to check their flour's characteristics. One of the values given by Alveographs is the p/l value. l value is an index for extensibility: how much can the dough be stretched before breaking. p value shows how hard is to give the dough a shape. p/l gives an idea on how the dough holds the shape it's been given. Flours with p/l≈1 are said to give "equilibrate" doughs for bread, as they are easy enough to give a loaf shape, and they will keep that shape once given.

Pizza flours should have a p/l≈0.5, as it means the dough can be stretched to a big disc shape, it won't tear, and won't stretch back to a smaller disc.

For long fermentation time, a high W value is desireable: W=280, 300 or 320 are common values. W is not always related to p/l values, and it can be undesrtood (informally) as "how much gluten the flour has". As gluten in a dough gets degraded with time, a lot of it is desired initially in the dough to assure there will be enough at the end of fermentation, several hours (or days, if refrigerated) later.

Forget about those 00 in Italian flours. It really only means the finesse of grounding. For pizza making I try to use strong flours with a p/l value close to 0.5, albeit I've also used strong bread flour with good results.

How can I get flours with those characteristics?

There are some specific pizza flours. Some Italian makers (with no specific order) are: 


Caputo
Spadoni

You can see how W value is related to their recomended fermentation time.
5 stagioni

If you check the p/l value you'll see it's 0.6: right for pizza stretching.


If you can't get specific pizza flour, you can also try with flour specific for croissants, as they will also be strong and stretchy.

I've never eaten nor seen Chicago style pizza, so I can't help with flours specific for them, but I guess the guidelines given above should help.