We used to stay onsite, and even though we had our car there, for the most part, we took the buses. Last summer, we stayed offsite, so we had to drive, and I learned something. I could drive, offsite, and get back to the house we were staying at in pretty much the same time it would take to get a bus back to our Disney Resort, even from MK. So, my answer is going to be this: If you think you will be tired enough at the end of the day to not want to drive, or you think you may be partaking of enough adult refreshment during the day to not want to drive, then take the bus. If you want to avoid waiting in lines, sitting, or standing, on a bus where riders are packed like sardines, and then walking a mad mile from your bus stop to your room, then drive.