I haven't stayed at either one, but I have visited them both.
I think it depends on what you're looking for.
I'm not a big advocate of paying premium dollars for "magic", but the Animal Kingdom Lodge is such a transporting experience. The restaurants are both amazing, albeit somewhat pricey. I can't comment on the Mara, because I haven't been, but I LOVE both Jiko and Boma. The smells in the lobby, the GORGEOUS wood floors, and the attention to decorative touches that permeate every aspect of the public areas really makes you feel as though you are in a different place. Even the walk from the parking lot is transfixing. The lush vegetation that seperates the porte cochère from the parking is really pretty.
However, the Swalphin has a lot going for it. We stayed at the Beach Club, and I fell in love with the general area. It was SO nice to be relaxing in our room, and feel like a nice dinner and just stroll over to EPCOT, and have a relaxing dinner at Marrakesh. One morning, I wanted a little something special for breakfast, so I went to the Boardwalk bakery and got some great coffee for my wife, and some WONDERFUL pastries for breakfast. It was a very calm morning, and GREAT to watch the sunrise over Crescent Lake. And you know that SEA of humanity you have to fight to get out of Epcot after Illuminations? SO much more tolerable when you can leisurely walk back to room instead of fighting crowds to the front, and then in the bus lines. (Or fighting traffic if you drive your own car)
I don't know if you'd stay at the Swan or the Dolphin, but the interior of the Dolphin really is a neat experience. It's like walking into a big circus tent. There's some waterfalls in the breezeway between the doors and the main lobby, and it just felt very relaxing. And I have stayed in other Starwood properties that feature those heavenly beds. Oh. My. God. It's so worth it just for those dang beds!!!!
I believe the Swalphin rooms are also larger than what you'd get at the Animal Kingdom Lodge.
So if you're looking for the magical experience, and don't mind paying a little more for it - I'd pick Animal Kingdom Lodge.
If you're looking for comfort and unbeatable convenience at a more reasonable price, I'd pick the Swalphin.
But again, that's based on observations as a visitor - not a guest.