I have been using Big Apple for nearly 15 years with a frequency of about once a month going to LGA or JFK. Setting up an airport pickup is a bit more complicated and since I seldom know much in advance of my arrival, I seldom formally set up the pickup and just jump in a yellow jalopy.
However, they are quite a reliable backstop if you arrive at one of the NYC airports and there are no taxicabs outside. They have cars which will arrive within 10-15 minutes of your call and they have always been completely reliable. In all the time that I have used them, they have only been late to the pickup twice (both times calling and letting me know of the delay).
I can say that every other service that I used before them had a serious FAIL within a year after I started using them and as far as I am concerned, this service has been relatively bulletproof.