We have rented a car, used a Town Car service with a grocery stop, and used DME.
I prefer DME to all options.
When we rented we found that the car spent most of the week simply parked in the hotel lot. We seldom leave Disney property and we prefer to use Disney transportation. Not having to drive is part of the vacation for us. DME saves us a lot of money.
The other thing I do when using DME is think about using cabs for some of our resort to resort dinner ADR's. A cab or 2 for dinner is still much cheaper than renting a car for a week, and we don't need to worry about a "Designated Driver" for the return trip.
As suggested, once you are there if you really feel you need the car you can rent from the property - or nearby.