We have rented a car. We have also used QuickSilver. They will give you a 20 minute stop at a grocery store if you do round trip. This can save serious money if you buy cases of water and breakfast items. Sometimes we don't like to give Disney the control using DME because the waits can be maddening with DME.
We used Quick Silver the last trip (Dec '16) because we opted for an off-site property. Our driver was very professional and we loved the 30 minute grocery stop. I would highly recommend them. I've never had an issue with ME lines, but we usually stay at Deluxes and I will say I have noticed the lines for the value resorts are usually much longer. I personally have never had to wait for ME...we've always just walked right up and had no wait. I did enjoy the personalized aspect of using Quick Silver.