I have used towncars about 6 times now, and DME 3 times. The only time I got to my resort faster using a towncar was the one time I flew with carryon bags only. That time I got to my resort in about 50 minutes.....30 minutes from the airport to my resort, and about 20 mins from plane to towncar driver and then to the car.
Otherwise it has taken me, on average, about 70 mins to get from the plane to my resort. With a towncar, and checked baggage it took about 65 minutes. I know there will be times when I will use a towncar service, but for the most part I will choose to save that $100 (or so) plus $25 tip and use it for a few meals at WDW.
But, for those who choose a more luxurious experience, as well as that 30 min stop for groceries (I use a grocery deliver service that delivers to my resort, charges about $15-20 fee), then a towncar service is the way to go. But I find the DME buses to be quite comfy, not crowded, and efficient, as well as free. And lets not get into the whole 'but is it really free' discussion!!!!