MK to Epcot is an easy two monorail trip during most of the day. It is at closing time for MK when it can be a slow trip and that is generally true no matter what form of transportation you choose. When you have tens of thousands of people departing all at once the lines get long for the monorails (and busses and even those cabs). During most of day, it is a 20 to 30 minute monorail trip including wait, at closing it can go to an hour or even more depending on where you end up in line for the MK monorail and then the one to Epcot from the TTC.
As to leaving a park at closing and to which resort is fastest, it really depends on park and resort. Examples: MK to Contempary is quite fast because you can walk it; to Grand Floridian and Polynesian it is not bad because of monorail; going elsewhere by boat or bus can take quite some time; similar at Epcot or MGM -- if you are going to BoardWalk, Yacht Club, Beach Club (and villas), Swan or Dolphin, you can walk and thus avoid long lines for boats (the other option); going elsewhere will usually take quite a bit of time depending on where you end up in line to wait for transportation.