I've used most of them and have alternated from being very happy to having any one of them just not show up. One of the drivers explained to me the system. They get these placards for more than one service. So if the 6'es have more calls than the 7'es, they will pull some drivers who might work for the 7'es more often. He shows up at the airport with the sign for the 6'es.

So any one of them can be hit and miss.

Once, after having a couple of services not show up I got friendly with a driver from a new service and he gave me his personal number. Assured me that he'd always be there if given enough advance notice. Worked great a few times. But eventually he too did not show up once with no phone call to warn me to find another drive.

So it seems to me no matter what they are all kind of pot luck. Unless maybe the expensive limos where you could expect a different class of service.

Having said all that, 90% of the time, they do show up just fine.