For MK to WL, the nicest way (IMO) is the boat. But the bus would probably be significantly faster.
From Epcot to Poly, the easiest (and probably fastest) way, IMO, is to take the monorail to the TTC and then walk from the TTC to the Poly. It's a 5-minute walk with no waiting versus walking down a ramp, back up another and waiting on the resort monorail.