Theone thing that is near 100% agreement is to take the bus to MK. less than 15 minutes from the time you get on the bus.(may wait up to 20 minutes for the bus, bus usually not that long).
The reason almost everyone takes the bus to the Magic Kingdom is that you can't park there. Only Disney buses are allowed near the MK entrance. All other vehicles (including taxis) must go to the TTC. From there you might have to take a tram (depending on how far back you are....the parking lot is HUGE) and then either the boat or monorail to the MK.
IMHO Disney does a great job in getting people to and from their theme parks. Best advice is NOT to exit any park immediately at park closing. There is always a sea of people heading out so it's better to either sit or shop or just wander around for a while. We did this in June after Wishes at the MK and by the time we got to the bus stop everything was quiet with no crowds of people.
By bus, I'd expect at least a 30-minute commute door-to-inside the park travel time, when you include waiting for the bus. On crowded days, 45 minutes is more realistic.
I agree with the above posters, definitely ride the bus to MK, and avoid the TTC with its trams and ferries, that pretty much double the amount of time it takes to get to MK.