My family usually stays at the BW, but we've stayed at the BC as well. In both cases, the walk to Epcot is really easy.
Boardwalk dock to the International Gateway is 0.36 miles (640 yards), while the Beach Club main entrance to the International Gateway is 0.23 miles (400 yards).
From the Boardwalk dock to DHS' main entrance is 0.8 miles (1,400 yards), while the Beach Club another 0.4 miles (so about 1.2 miles (2,100 yards) in total).
For reference, it's about 0.8 miles from Epcot's main entrance to the American pavilion at the back of the WS.
If you're staying at the BW, it's very convenient for either walking or the boat. You're the last stop before going to Epcot and the first stop to be picked up on the way to DHS. The boat ride takes about 35 minutes (from Epcot to DHS) and runs until one hour after park closing (if DHS closes earlier than Epcot, they stop going to DHS one after DHS closes). The boat goes from Epcot -> BW/BWV -> BC/YC -> S/D -> DHS -> S/D -> BC/YC -> BW/BWV -> Epcot.
For the Beach Club it's actually easier to walk to Epcot than try and take the boat. The dock is over by the Yacht Club, so you actually have to walk away from Epcot to the dock to catch the boat. It's not a long walk, but it feels like it because you're heading away from your destination!
