My own experience (which is in the western half of the US), is that “pizza” is the most common term, both when describing the dish and as a unit. I would say, “let’s get two pizzas”, not “lets get two pizza pies”, “let’s get two pies”, or “let’s get pizza. How about two pies?”
I occasionally hear “pizza pie”, but this is very rare. “pie”, as a standalone, I have never heard “in person”, but have seen (once) on tv.
Specifically, I saw a stand-up comic on tv many years ago. I believe the comedian was a New Yorker, and he talked about an experience in college when his new roommate (who I believe was a Bostonian, or perhaps from New Jersey: it was a long time ago) suggested that the two of them “split a pie” for dinner. The New Yorker was baffled, imagining that his roommate had a sudden hankering for, say, an apple pie. He agreed, though, no wanting to get off on the wrong foot. His new roommate later showed up with a pepperoni pizza, and (of course) he then realized pie meant pizza.