I have used Clives, Juta and Alfreds, but of the three most trips are done with Juta. Clives was great, and I got a discount on a Mayfield Falls trip since I had booked round trip airport. A couple of times I was with another couple in the car, and once by myself.
I did my a private transfer last May with Alfreds- only the second time I had done private--the other time was with the Seastar driver. Private was great because we stopped for a big grocery shop in Mobay, stopped at Biggas, and stopped at half moon on the way to Negril.
But that said, I am usually on a really tight budget and Juta works well for me (I have used them about 7 or 8 times) I never have to wait long for the other passengers and generally grab a red stripe and a patty while I wait. What I have found to be my least favorite aspect of Juta is most often I have to leave way too early for the ride back due to AI people catching earlier planes. I like to prolong my departure every bit that I can and my flights are usually in the afternoon. Also sometimes the other people on the bus don't want to stop for food or refreshment on the road--let alone bathroom breaks.