For MK let me suggest the ferry dock at the TTC. They pipe in the music, and you have a pretty much straight on view of the castle. And if you have a car parked in the TTC parking lot, you can be on the tram back to it before the hordes start descending from the monorail and ferry to do the same thing.
If you don’t have a car, I would suggest taking rideshare from the TTC back to your resort after the fireworks are over. Again, you’ll be able to request one before so many other people arrive at TTC to do the same thing. (if you’re not staying at a monorail resort, you can take Disney transportation from your resort to MK, then ride the monorail or ferry to the TTC before the fireworks begin.)