Beach Club all the way. Have stayed at both (also through SoG), and I believe they are not in the same league. When I stayed at Dolphin's sister hotel Swan last year, I was dismayed at the shabbiness of the rooms. The resort is beautiful ouside and lobby is nice....but when is comes to the rooms.....it was BADLY in need of a renovation. I would not stay there again, and I'm not generally a whiner. Like everything else on property except Bungalows at Disney Institiute.
BC is fresh, with BEAUTIFUL decor. It's walking distance to EPCOT is awesome. (Dolphin is walking distance too, but significantly further away.) Restaurants (including those at YC) are also much better. THE POOL IS THE BEST ON PROPERTY!!!
Swan and Dolphin are Westin Hotels, not Disney Hotels. I don't think this means S & D have to be a lesser experience. But they are.
My strong opinion: $130 at Dolphin is not a great value, and $170 at Beach Club is a good deal.
GRAB THE GOOD DEAL.
Sorry Swan and Dolphin fans.
DisneyVirginia