We've stayed at both, the Swan several times and the Dolphin this past May. We're staying at the Dolphin again in December and I can't wait.
We've enjoy staying at both resorts but something about the Dolphin made me like it more, maybe the atmosphere and convenience with Tubbi's. I thought I wouldn't like it as much as the Swan when we decided to stay there but ended up liking it more.
The Dolphin is quite a large hotel but that actually makes it fun. Our room was in the last west wing with a view of the EPCOT fireworks, BW, the lake, the Swan...it was cozy and fairly quiet because it was at the end of the hall although this did make for a long walk to the elevator. But, I preferred this location since it was quieter, plus it had an awesome view. And, when we got off the elevators Tubbi's was just right around the corner.
The rooms are physically similar, but the Dolphin has 2 double beds and the Swan has to queens. The Dolphin has one sink and a vanity outside the bathroom whereas the Swan has 2 sinks. The Swan is more intimate and smaller which is nice. The transportation from both is pretty much the same.
It's all the matter of preference. I was very skeptical to try the Dolphin after staying at the Swan so much, but was pleasantly surprised how much I liked it ...almost more than the Swan...
