It kind of depends on where you're going in Epcot, doesn't it? I love walking, but people who don't should know it's well over a mile from MGM gate to International Gate, and nearly 2 miles from MGM gate to Spaceship Earth.
The boat will get you to International Gate, probably the same day. But if you're going to Future World and don't care to walk 2 miles, the bus is by far the best option.