Well, both are completely different in terms of theming.
At the WL, it really feels like a big log home in the woods. Very woodsy, warm and welcoming. You don't feel like you are in Florida at all! Disney has done an excellent job in transporting you to another time and place at the WL!
The Dolphin is tropical, light and fun and says 'vacation' at every turn! Palm trees, beautifully themed tropical pool, and some great views of Epcot and MGM and the fireworks from Illuminations and Fantasmic.
The Dolphin ranks superior in the transporation department! It seems like at the WL, it's the last on the circuit or something, even though I know it's not true. It just seems to take forever to get somewhere, with the exception of the MK, where you can boat over.
Having stayed at both, I can honestly say I prefer the theming and transportation at the Dolphin and Swan, but I am glad I got to experience staying at the WL. If you don't stay there, I recommend a visit, even if it's just to walk around the lobby!