i have used Tiffany several years ago, but they have changed hands. We are going in June and I would be interested in the answer to this question myself.
We go to WDW every year and for the past 2 years we switched to FL Tours. They are wonderful and I have never had any problems whatsoever. We used Tiffany for many years prior to 2001, but I noticed their service went way down hill. Not at the airport when we arrived (happened 2 years in a row, had to call and was told both times that our original driver had car problems and they were sending someone else). Also had issues with them picking up as well - again the same "problem" mentioned above. They might have improved since but FL Tours hasn't given us a reason to try anyone else.
We used FL Tours on April 10 and April 17. We were 45 minutes late getting through customs, but the driver was waiting for us exactly as planned. He was very courteous and talked freely with us during our trip. On our return trip, the driver was there 10 minutes early and was very nice. He was not as talkative, but I think he sensed our disappointment in having to leave.
I highly recommend them. They even called us at Pop to confirm the departure information.
Very good service and much better than being at the mercy of Mears.