Marsh view is a great idea for the reasons already posted. You may also need to request a third floor, however. A few of the buildings with marsh views may have filtered views through the trees and greenery on the first and second floors. Marsh views also face west, thus lots of direct sun in the summer afternoons can make your balcony a bit hotter if you plan to use it during that timeframe.
You can also consider the east facing views of the harbor. While not directly on the harbor (seperated by the driveway and some trees), the glimpses of the beautiful boats are also pleasant. The only views I personally don't care for are overlooking the pool, though I understand these are covetted views by many long time visitors.
Regardless, you really can't go wrong since this is a very beautiful resort, I have found all of our views peaceful and private and we've stayed in several buildings.