If you're in the World Show Case or at the Garden Grill I would say walk to the International Gateway, then follow the walkways to the Boardwalk, and then to HS. It's a long walk for most people, but you don't have to wait on a bus or a boat. My family has stayed in the BW/BC/YC area many times, and walking to HS from that area is faster than waiting on the boat and then riding along as it docks at other locations on average.
This all depends on your level of physical health since you will be doing about 20-30 minutes of walking depending on where you start. By the time you walk from Garden Grill to the bus stop you are gambling on whether a bus is arriving at the same time or shortly there after. If you just missed the bus it could be another 10-15 minutes before you see another one arrive. It's all up to how you want to travel. Granted the bus will have air conditioning on hot visits.
We love staying in the Epcot area because of the walking access to two of the four parks.