We use a combo: rental car and WDW Transportation. I prefer to use DisTrans; if we drive, I'm the driver, so I enjoy the break, and it IS part of the magic to us. That's why we like the Monorail resorts, particularly the Polynesian - using DisTrans is so much easer there. "Por favor, ...."
That said, there are times I take the car because it makes things easier for us. TL/BB, for example; it's nice not to have to lug bags on the bus, and when we're done it is nice just to hop in the car and head "home". Also, as has been noted, DisTrans just doesn't work for resort-resort[-resort] routes.
To summarize: We love and prefer DisTrans, but a car gives us additional vacation freedom and options.
Erick