I'm going to say VWL and OKW. At OKW, you can be very close to any number of bus stops. The only issue is being sure you are on a ground floor or elevator building. If you are across the street from HH, you are VERY close! We loved building 13 for that reason! At VWL, you will close for buses, but as mentioned, quite a walk from the boats. That shouldn't matter though, because If I remember correctly, you can also take the bus to MK.
BCV is quite a hike and uphill for elderly people wanting to go into Epcot. Also, if they are going to MGM, the boat dock is all the way over by Beach Club, again a hike. BWV has that whole long hallway thing going on. Only a very few units are close to the elevators, and even then, you have quite a hike out to the boats. Buses might be a bit closer. SSR SHOULD be about like OKW, but unfortunately, we did not find that to be true. Even though the bus stop was near our end of the building, it can be quite a ways for the mobility challenged. The advantage at SSR is that you will always have an elevator, and you could request close to a bus stop. The problem is, we found that at SSR, often the shortest route to a bus stop was accross grass, and that's not easy either.