We have timed it out repeatedly, and find that driving ourselves is always the best option for HS, AK, and Epcot. For MK, it's a crap shoot. When leaving MK, if you drove to the park you have to take either the ferry or monorail back to the TTC, and then either walk or take the tram to the parking lot. If you are taking the bus, you get to stand in the queue. I've waited 45 mins in the queue for the bus to POP 3 times. That is NOT fun at the end of the day. We usually take our time leaving after the park closes, and it's easy to get a ferry/monorail/tram, and then drive back to our hotel.
There are things to take into consideration when trying to make this decision. We usually stay at the value (or occasionally moderate) resorts so parking lots are very close to our buildings, which is very convenient at the end of the day- but I hear that not the way with the deluxe resorts, so you have to consider the walk from the parking lot to the building at the end of the day- although the walk from the bus stop (at values/moderates) to your building at any resort can be long. We have also learned that getting a seat on a bus is a very rare occurrence, and you cannot count on someone offering you a seat if you are carrying a sleeping child. Are you able to balance both a sleeping kid in your arms and a folded stroller while standing on a moving bus? Do you mind being packed in like a sardine with other overtired, sweaty, hot people? We usually prefer to go out to our car, plop the kids in their carseats, grab a cold drink from the cooler we have stashed in the back, and drive to our resort while sitting in quiet, a/c comfort. When at all possible, we rent a car and drive ourselves to the parks.