I can't speak to the pools, but I'd choose one of the copley hotels as they have a great central location.
Thank you. I'm more concerned about the pool differences and while I know these aren't water parks, I'd like to choose the one with the bigger pool.
The Sheraton's pool is in a glassed in area with a retractable roof. It is designed to handle the "summer crowds". Obviously the roof willl be closed in the winter.
I do not know how it compares to the size of the others ... sorry.
We have enjoyed the Marriot Longwarf pool with kids and it is very close to Quincy Market, restaurants, the T and overlooks the waterfront. No experience with the other pools but the hotels you mention are excellent.
Your best bet is probably to call each hotel and ask how big their pool is.
The Intercontinental has a pretty good pool. A little walk from Back Bay, or a short T ride.
I highly recommend the Sheraton Back Bay. Sadly when I stayed there in September the pool was closed for maintenance but it looked beautiful and large (my room overlooked it). I spent 10 days there and the staff could not have been nicer! I read horror stories about the staff before going but they were honestly the best group I've interacted with at a hotel. The location is pretty good and there are a lot of restaurant options in the area. The big selling point is that you can access the T station from inside (2nd flood, walk into the Prudential Center and then follow the signs).