I prefer the Dolphin to the Swan, but there really isn't much of a difference. The lobby area in the Dolphin is far superior to the Swan, and I also like having the convenience of Tubbi's right downstairs rather than having to walk across to get to it. The resort is quite large.
The last time we went 12/25-12/31, we had a resort view room (8133). It was actually larger than a regular room with two windows. There was one section the size of a regular room, and then one section off to the side with the beds. Basically one part of our room was pretty much empty except for the armoire and armchair, creating a huge room! It was directly next to the elevators, so there was no long walk to the room, and as soon as you walked out of the elevators, you were right by the exit to the bus stop.
Both hotels are great, but if you go during a peak time of year the Swan might actually be a better choice since the buses stop at the Swan first, which creates many already full buses stopping at the Dolphin.
The Westin/Sheraton thing doesn't make much of a difference at all. They are all the same Starwood company, and the rooms are identical at both hotels.