One's a moderate, the other's a deluxe. Two different classes of resorts. I have at POR, Alligator Bayou, thought it was great. Very relaxing grounds, walking paths, nice food court. I have stayed many times at the S/D, mostly the Swan.
Dolphin is in the heart of Disney, situated in walking distance or Friendship boats to both Epcot and the Studios. Also walking to the Boardwalk and all it offers in dining and entertainment as well as the Y&BC resorts, nice dining there. Also a pool area second to none and equal to SB.
If my pick, the Dolphin. Here is a good information thread.
http://www.disboards.com/showthread.php?t=3264274