I agree with sharadoc. BWI/BWV are the most centrally located if you want to walk to both DHS and EP. We stay there a lot for this very reason! If you want to be a little closer to the DHS path, consider booking BWV.
BC is the closest to EP (like, really really close!), but is a little farther to DHS. If staying at YC/BC, we'll walk to EP, but boat to DHS unless it's evening and we are walking back from DHS and want to visit the Boardwalk.
Swan is very close to the DHS walking path and Swan/Dolphin are the last boat stop going to DHS and first stop coming back. Dolphin is kind of the furthest from both parks (at least it feels that way). It has this windy path you have to go on before you start walking past YC to head to EP.
Anyway! Long winded way to say, yes, all 5 are close to EP and DHS, but BC, Swan and Boardwalk are most walkable with Boardwalk getting my vote for most centralized! And it's a GREAT resort!