For the past two years I have stayed at Ai Cavallieri. It is a 4 star hotel in the Castello Sestiere. It is a very quiet location near the Campo Santa Maria Formosa and Campo Santa Marina. The hotel has a water landing and it is a very convenient water taxi ride to the airport. Last month we had to leave our hotel at 0430 for our 0620 fight to CDG.
The hotel is beautifully maintained and has a warm, welcoming staff. I find the location to be extremely convenient to any part of Venice. You will definitely not encounter hordes of tourists with selfie sticks.
I do not recommend Boscolo. I stayed there several years ago and the rooms are very hit and miss and quirky. I believe it is now a part of the Marriott Autograph collection. It is, however , in a good location.
I have stayed at Hotel Ai Mori D'Oriente several times. It is just in front of the Boscolo in Canareggio. I am very fond of this area. Only drawback is that you will find yourselves walking the dreadful Strada Nova many times.
The only time I have stayed in Dorsidoro is when I rented an apartment for 2 weeks. Very nice area. My preference is still for Ai Cavallieri in Castello.