I'll also be staying at the Mandarin Oriental, a bit later in July. I don't know too much about it, but it's very convenient for where I need to be.

The view of the fireworks from your room will depend on the orientation of your room.

However, if you book a suite or a club-level room, you'll be able to use the Club Lounge. That sounds like it would probably have an excellent view of the fireworks display. From the Mandarin Oriental Web site: "And the view from the Club Lounge across the city is breathtaking, taking in the Bureau or Engraving and Printing and the FCC, to the Washington Monument and beyond. There is also a terrace, and even two telescopes to ensure you make the most of the view."

In terms of getting there from the New York area, I would definitely take Amtrak over flying or driving. (I've tried all three options. I grew up in D.C. and frequently visited New York.) If you live extremely close to one of the airports, flying is a viable option. However, from Manhattan, I'd highly recommend the train. Many of the trains take well under three hours from New York Penn.

Once you arrive into Union Station, you can either take a taxi or Metro to the hotel.