I would definetly drive my own car.
Disney buses work, but at park opening and closing the lines are looooooooong, it is a lot faster to wait for the monorail or ferry and walk to the first tram stop in the parking lots.
September is really slow, so dh and I found that if we got to MK before 9:30 we would park so close that it was easier walking to the turnstiles than to tram stop, especially with a stroller.
And sometimes the bus routes have problems, last may 5th we waited for an Epcot bus close to 50 min outside ASMu, so instead of arriving at the park before opening (I arrived at the bus stop at about 8:35) we got there about 9:35 and the lines to Soarin´ Nemo, etc were already long.
And you can always decide to hop from one place to another in the car, which is faster.
Oh, and using Disney transportation to go to DTD is a complete PITA, if you don´t use your car all the time, at least use it to go there.