Definitely IASW for fireworks! I think most of the "tourists" don't realize it goes back there, so line up on Main Street. The IASW crowds don't build until they start roping stuff off and people are like, "Hey the parade's coming, let's watch." We stumbled upon it when coming off of IASW last time and were really up close and personal...my girls got lots of kisses blown at them from Princesses. Main Street is kind of overwhelming during the parade....people everywhere...people trying to exit the parks between floats...and just a lot going on.
The hub is the most immersive experience for fireworks because there are some that go off literally around you in the circle. The view is pretty good anywhere down Main Street though. We've timed it where we get off the train right as they start and watched from the platform up high. It was nice, but we couldn't see Tink fly.