I completely agree with everything posted so far, but another very important factor is cost. For the LARGE volumes of refrigerant used in the large facilitites described before, common household use freon would be cost prohibitive. Price a cannister of r-whatever and multiply the volume to equal a ton, and compare to approx. $400 a ton for anhydrous ammonia.
No argument about cost - nitrogen and hydrogen are a lot cheaper than fluorine.
While ammonia may only be somewhat better than freon, on a large intsallation that small difference can still add up to some serious bucks.