OK, here's my point of view on the subject of driving versus the bus. Every time and I mean every time we go to Magic Kingdom, I park at a resort and use the bus to Magic Kingdom. And it will be faster!!! If you drive, you will park and then probably walk a good distance to the tram. You will wait to get on the tram. Then the tram takes you to the TTC. You wait for either the monorail or the boat. Even if I wait 25 minutes for the bus, it will be faster. Once you get there, you walk right into Magic Kingdom. And even a longer and slower way from the Y&B would be to walk thru Epcot. I speed walk and let me tell you, with no crowds and a clear field, it would take me at least 20 minutes to get to the front of Epcot and that's really really moving. Then you would wait for the FIRST monorail that takes you to the TTC. Then you get off that monorail and wait for the second monorail that takes you to the Magic Kingdom. Absolutely the longest possible way to get there. However, the kids that love the monorail and are being pushed thru Epcot in a stroller probably would vote that way every single time.
I would NEVER drive and park there. However, if I was staying at a resort and in a real rush to get to Magic Kingdom (for whatever reason), I would take a cab and have them drop me off at the Contemporary Guard Gate. Then I would have a 5 minute walk into Magic Kingdom.