As pp said, fastest is to drive. If you don't have a car, I recommend Uber-ing from PO to the Boardwalk resort, costs less than a taxi.
-OR, you have to take 2 busses, most logical would be take bus to DHS, then walk, or take another bus or the boat. NOW, you do have to be CAREFUL with the 2 busses thing, sometimes they're not running TO the resorts that early in the morning. We ran into that problem trying to get to 1900 a few years back, so if you do go this route, definitely go to DHS as it's walkable from there.
-Remember that if you bus to Epcot, you have to walk THROUGH the park, thus, it has to be past 9am opening time, and YOU MUST HAVE A PARK HOPPER, if you're not returning to Epcot later that day, as it counts as a park entry.