I've used these guys twice to get to the airport. First time: missed the bus at 6:45am and called them from a parking lot - they were there promptly to take me to my flight. Second time: called the night before to schedule a morning pickup. The taxi went to my neighbor's house, but it was clear that he was there for me so no big deal. Both were quiet and not talkative.
The only thing is that they seem to have trouble figuring out the rates vs. where they picked you up - the first one charged me the wrong rate (according to their flat rates posted in the back of the taxi) and the second couldn't figure out what rate it was supposed to be. $14 flat rate to the airport, varies a little depending on where in CU you are.