Hello-
I have used Tiffany Towncar for our last 3 trips to Disney and had very good service with them.
For this trip I had a bit more "complicated" itinerary requests and sent them to Tiffany, Yourride, and Florida Tours. Tiffany was not very accomodating via email. Yourride never wrote back and Florida tours offered a very quick response time (and they are a board sponsor).
I mentioned that I am a DIS member and they quoted me a rate of $40 one way or $75 round trip to the Hard Rock Hotel. It is also expected that you will tip your driver 20%. When you rent a towncar, you agree to a price upfront from point A to point B so if the traffic is particularly slow, you still pay the same rate.
Contrarily when I asked Yellow Cab company for a quote they said the minimum cost would be $35 one way but they do charge you for sitting in traffic so I am much happier to just have someone pick me up when they say they will and not stop anywhere else along the way (yes, Mears will do that).
Also, you can put it on your credit card and that's less cash to carry.
Yes, if you ask in advance most towncar companies will allow you a 30 minute "courtesy stop" at a grocery of their choosing.
Brenda