1) Are you on a budget? What do you want to spend on a room per night?
2) Do you need to get wherever it is you are going in a relativiely short amount of time?
3) Do you prefer one park over another?
First, see if you can qualify to stay at S/D with a discount. As a guest of both locations, I prefer S/D because of:
1 - location, location, location!! (within walking distance to Epcot, MGM, and BW)
2 - rooms are slightly larger with a few more amenities
3 - although S/D is NOT a Disney-owned resort, it enjoys all the same perks that the other Disney locations have (with the exception of the credit card/room key priviledge)
4 - the only time we used the bus was when we visited AK and MK; the walk was a quick one with the bus stop directly outside the lobby (one thing I absolutely HATED was the extensive walk to and from the bus stops to our room)
5 - I also would rather stay at a resort which has an indoor hallway as opposed to an outside balcony/corridor
Good luck with your decision!!!