I have never stayed at Pop, but I love, love, love the Swan. The ease of getting to Epcot and MGM (either walking or boat) is unbeatable. Also you are just about a 5 minute walk to the Boardwalk. For your family makeup I think that the Dolphin might be a better choice as it has a more festive atmosphere, while the Swan has a more subdued elegance. Given that the S/D are deluxe resorts with all the amenities (and then some), wonderful attentive staff and comfortable, well appointed guests rooms, I would certainly pick them! Don't forget to join SPG (Starwood's reward program) before your visit for additional perks. Just keep in mind that they are not owned by Disney, therefore no Mickey toiletries or Mickey wake-up calls, no room charging in the Parks and you always run the risk of having highly visable conventions. Also don't forget to calculate the $10 resort fee and if you are bringing or renting a car, the $7/day parking fee. These things can really add up and sometimes make the low teacher rate not so attractive.
Some other advantages: Grotto Pool, Starbucks Coffee, Tubbies Buffeteria (open 24 hours) heavenly beds, top notch housekeeping and generous room upgrades (depending on availabilty)