We have stayed at both and are going back at Xmas. The reason is simple, great Epcot location for often about half the price of a Disney deluxe. Can't beat being able to walk to and from Epcot and DHS at really busy times.
Yes, the Yacht & Beach is nicer, and the rooms are bigger but, unless you get free disney dining and/or a good discount, S/D are generally better value.
We don't tend to use Magical Express, and S/D still get EMH and disney park transport. Not too bothered about the disney "magic" at the hotels, we just want good rooms and service at a "reasonable" (for WDW) price.
Downsides are c$10 resort fee to include internet and bottles of water (similar to Disney's internet charge), plus a similar daily fee for parking.
We have sometimes had rooms with a balcony, and once had a lovely 2 aspect Epcot view room with balcony at the Swan.