What's great about pizza in New York is the spontaneity. After a night out there will always be somewhere nearby with a pretty good slice of pizza. The best pizza I had while living in New York isn't any better than the best pizza I've had in Seattle but the average slice was much better.
There's so so many places honestly. I could rhyme off a half dozen more on this list that some new yorker would say is "the best".
But coming from out of town your expectations are probably sky high. If pizza is high on your list, go for gold. It's a fun thing to do in the city. Also you need to treat both categories separately - slice, and whole pie. different game.