I'd once took the Disney architecture tour. They said Grave designed the hotel, so that Swan is the quiet elegant section, and Dolphin (aka Tuna the fish) is the festive one. So the lobby is much more chaotic (by design) in Dolphin side. And it shows. The wait line and the lobby looks busier to me ever since I know the back story.
That said, it really doesn't matter that much. It's a great location, walkable to Broadwalk (ie, restaurants and reasonable nightlife). I found both hotels to be a bit tiring. But you get SPG points, and it's the individual rooms that count, whatever you're paying for.