The most direct route is a cab but .....
As far as Disney Transportation goes ... it depends on what time you are going and how much you want to walk.
1) Take bus to MGM and then take the boat to Boardwalk or you can walk the path to Boardwalk.
2) Take the bus to Epcot, go into Epcot, walk through Innoventions area to the International Gateway and then take a boat or walk to Boardwalk.
3) Take a bus to DTD and then take the bus to Boardwalk.
4) Take bus to MK and then a bus to Boardwalk.
Hope that helps.