We have rented a car, taken Mears and used Your Ride.
The town car servioe was the best all the way around.
Most town car services allow a free half hour stop at a store. Just make sure you ask about that up front on the ressie, if you go that route. I always used my half hour stop at a Disney outlet store right outside of WDW. I can do a lot of shopping in one store in a half hour.
Rental cars are necessary if you plan to go off site.
If you don't know your way around, I think a rental is more trouble than it is worth.
It would also depend on when you go to WDW. If it was during a busy season, then I would be more inclined to rent a car. But even with that you still are taking shuttles to and from the parking lot/park.
Staying anywhere on property and taking a bus to and from DTD is a long trip and a hassle. Not hardly worth it.
To me, it would depend on how pressed for time I would be, how often I planned to go to DTD, and if I wanted to go outside of WDW.
Almost all my WDW bus experiences have been good. But the bus service for our May 2002 stay at POR was horrible. And a rental car would have been a godsend.
One January, we rented a car for a few days and we were happy to get rid of it. I think it really depends on many factors. And you may plan on going off site. But your days will be packed already at WDW.