I have stayed at the Dolphin four times with my family and it is GREAT!! Great location, great employees, and AWESOME BEDS!!!
People always talk about how it's not a "Disney" hotel .....well I can't say I feel that way at all. You are in between DHS and Epcot, plus all the other Epcot resorts are a boat ride away!!! Add to that the fact that Fantasia Fairways is a walk across the street, there is so much to do!!!
I have visited SS and while I think it looks incredible, I have to say that the distance from all the various parts of WDW puts me off. We have stayed at OKW and while it is nice to have a little kitchen, I would take the location of the resort as first priority!
Either way, both are great resorts with many positives!!
Good luck!