I will say the Swan for sure. Dolphin is okay, but probably more kids and more activity than you may be looking for. The Swan lobby is more small and intimate, both the S&D have a lot of conventions, so you get a lot of adults there minus kids, and you can't beat all the dining that is within walking distance...dining within the S&D, plus the YC and BC, plus the Boardwalk, PLUS EPCOT! We love the location (and don't have kids). Also, the S&D both have quiet pools that are fairly quiet because many of the kids tend to go to the bigger pool in between the 2 resorts. We love walking to EPCOT and MGM or taking the boat.
I would also consider the Boardwalk Inn, but the deals may not be as good as at the Swan.
Good luck with your decision!