The Swan is considered “nicer” because it’s quieter as it’s not connected to the convention center. The Dolphin lobby, which is connected to the convention center can get chaotic. Swan also has less rooms which also contributes to less density.
Neither is really closer to Epcot. You have to walk from either to a central courtyard and take the same bridge across the water to the paths that go to Epcot (you can take either the Boardwalk route or the Yacht and Beach Club route). Both resorts share the same friendship boat stop and are equidistant to it.