Busses do park to park but not resort to resort.
The boat is slow between MGM and Epcot, but it's nice if you want to start in on the world showcase first. It does make three stops, Boardwalk, Yacht and Beach Club, Swan and Dolphin.
MK to Epcot, there's no better way than the monorail.
And the bus drivers are nice, once we were trying to come from down town back to epcot after the park closed, and there weren't anymore busses, so the driver took us over there, and made sure we got to our car before leaving.
It's very easy to park your car and not touch it for the rest of the trip. Although if you're in a big rush, a car is about the fastest besides the monorail.