Twice we have used Tiffany Towncar service for airport to hotel and back transportation and will do so in the future. It runs around $95 without tip, but if you have a Passporter's Guide to WDW, there is a coupon in the back...saved $8 I think. My Dsis has used them also and loved the service also.
What we love about TTC?
-the driver is waiting for us as we come down the escalator
-both drivers we had were very helpful...carried bags for us to the car and pulled the car to the curb for us so we didn't have to walk as far
-the 20 minute grocery stop allows us to grab bottled water, soda, coffee, breakfast foods and snacks to have in the room
-with the towncar, it's just our family so we get taken directly to our resort and directly to the airport...no stopping at others...no whiny children other than ours (lol)
-being the only family in the towncar means we don't get picked up as early as with DME or Mears
I'm not sure if I would use a towncar for transporting between hotels, unless the price was reasonable...a taxi might be cheaper depending upon the company. Best advice on this would be to contact the towncar companies and the taxi companies to inquire about a price. (I did this when I was searching for transportation for our June trip to DL...was told by DISsers taxi was cheapest way for our family of 3...when I called the DIS was right...of course...lol)
Hope this helps!