I think my opinion of DME is skewed by the fact that if we choose that, we are then at the mercy of the rest of WDW transportation which does not run as smoothly as DME.
In all of the bazillion times we've been to WDW we have used DME 3 times to the resort (meeting up with family who had a car), and only 1 time back to the airport (total disaster). The trips to the resorts have been smooth, it was the return and almost missing our flight that sours my perspective. We have used a town car about 4 times and everything was perfect. However, the remainder of our visits 99.9% of them we rent a car.