I've also gone back and forth between the two over the years (when one would piss me off, I'd switch, and then a couple of years later I'd switch back). I recently got screwed by Carmel, so I've sworn off them and will be using Dial7 going forward (or perhaps, Uber, as I screamed at the dispatcher on the phone telling him it was no wonder they were losing so much business to Uber...)

It was 10pm at LGA and a pretty long taxi line. So, from the back of the queue, I called Carmel and they said they could get me a car in 5-10 minutes. So we got off the line and went to wait curbside. No car after 15 minutes, at which point I called back, and they told me they were completely booked and didn't have any cars available.

And FWIW, the estimated fares on Uber were nearly twice what a taxi or Carmel/Dial7 would charge.