Here is the real important thing when you're dealing with the local taxi companies: If you need to get to the airport, and you arrange your car days in advance, call again about an hour before you expect to be picked up. THEY WILL FORGET. Not all the time, but often enough to call it common - and Checker has definitely forgotten some of my advance calls.
However, their drivers are good and their prices are reasonable. And if you arrive in the airport and they happen to have a car in the area, it's the best value for getting back to Nassau County.