It basically comes down to what kind of experience you are looking for. There are times I want that 'special, it's all about me' experience...then I use a towncar service. Sometimes, I would prefer to keep my money and put it towards something else. I don't stop for groceries, so that's a non-issue for me. If I need something, I'll have it brought in by a grocery delivery service for a $15 fee. I don't want to waste my time in the mini-mart, or the grocery store.
I have used DME 4 times now. I've used towncars 6 times. I love them both. It just depends on how I feel like arriving. I have found that the towncar doesn't get me to the resort all that much more quickly than DME...perhaps 10-15 minutes or so. BUT, if I don't want to deal with bouncy, trouncy kids on the bus, or risk being the third of three resorts stops, or having to wait for my luggage, then I can book a towncar.
Used DME two weeks ago...will be using a towncar in 3 weeks. Both work for me....depending on what I need for that particular trip.