If you're already in FutureWorld, then use the bus. But, if you're close to the International Gateway, in WS, you are better off going by either boat or foot. If there is a boat there, or one arriving, take the boat. The boat will stop at BW, YC/BC, S/D and then DHS. My friend and I got to the boat, just as they closed the doors. They wouldn't open them to let us on. So, we kiddingly shouted that we would beat them to DHS anyway. They laughed at us and said they would see who got there first.
Sure, they got to BW first, but after that...didn't see them again until we were at DHS, heading for the gates when we saw the boat coming down the canal..still had to come in and unload. We figured we beat them by about 8-10 mins.
The walk is nice, along a well-lit sidewalk. It's very well marked. But, if you would rather not walk, take the boat. Just plan on enough time...if the boat isn't there, it may be up to 20 mins before the next one comes along. Then, it will take 25 mins to motor from Epcot to DHS..so about 45 mins total time.