General thoughts- We've stayed at Yacht and Beach twice, poly twice, WL three times, Contemp once, and the Swan once.
1) We love the Epcot resort area. I'll walk around Cresent Lake while the wife puts the little ones to bed- much more going on than AKL or even the monorail loop.
2) For the family aspect- we would vote YBC again...BUT swan and Dolphin are offering discounts now when Disney is not...For similar money it would be YBC, or even BW (but the kids don't like the creepy clown slide). For a significant savings though???? Dolphin and Swan are great. That said, if this were a once in a long time trip, if possible I'd spend more for the imersive disney experience..with kids that is.
3) the doll/ Swan vibe....Less disney..actually quite swanky. While a simlar theme...Swan feels like a boutique hotel in NYC, while the Dolphin feels like a Vegas hotel sans casino. During our stay at the Swan, I actually spent a lot of time at the Dolphin for a lot of the reasons mentioned already- Picabus, etc...I would have booke thed dolphin this trip, but they are booked solid 1 night during our stay. not a big deal though- they are close together, AND you also have access to all the restraunts in the yacht beach and boardwalk hotels as well.
4) Both hotels have some floor plan quirks...the swan is confusing with its wings etc for guest rooms..the dolphin is confusing as their "main levels" and external entrances are spread over several floors.