Ditto what you are seeing, especially cindyinmpls. Two great options, both locally owned and operated. www.entertainment-plus.net and www.cancunvalet.com You can trust them both to do the job well and at a reasonable price. All private vehicles that you go from and to the airport directly, no stops and no sharing of rides. Go for it with confidence.
just booked my USA Transfers for May15-22. I have to say it was pretty darn easy and no money up front pay once you are in the car, I like that. So it's not like you can get screwed out of money or they have your CC on file to charge you even if they don't show up. From what I have read entertainmentplus is the way to go for travel or tours in Cancun and so far I believe it. See ya in May