I found the bus to be the most efficient method--every other way seemed either less direct or required more walking and/or a transfer, which were not popular with my party. We did end up driving a few times, but it didn't really seem like a time saver, particularly leaving at night, as you had to wait in a huge line for the monorail to the parking lot, and then a huge line for the tram to the car, unless you wanted to walk (as we did, through the thunderstorm.)
The other thing is that MK generally seemed to stay open longer than EPCOT, so when we did take the monorail over, we couldn't take it back again, as we wouldn't have been able to walk back though the closed EPCOT...