As far as walking goes -
MK - Contemporary is closest walk, but you can walk to Grand Floridian and then on around to Polynesian as well. Taking monorail or boats to any of them would be easy too.
HS - Boardwalk is the closest walk, but Beach Club, Yacht Club, Swan and Dolphin are all just a little bit further. Also can take the boats. You could also jump on the skyliner to Riviera or Caribbean Beach Resort.
Epcot - Pretty much the same as HS (just the other direction). Beach Club is closes, followed by Yacht Club, Boardwalk, Swan and Dolphin. Again, could take the boats pretty easy. Skyliner also an option from Epcot as well.
AK - You ain't walkin nowhere.