It would be best done by a vet. However emergency cases pithing is the fastest surest way. This would be very difficult for many to do however. The answer is going to change person to person. Freezing although not exceptionally fast or actually the most humane is still a viable option because it is easier to do than pithing so if a keep just cannot pith a beloved pet (understandably) and something needs to be done now due to a server trauma freezing is better than waiting for help.

emergency cases need to be done fast not wait if a person is not able to do the surest quickest then the next best option is in order. Pithing is the first choice but assuming a person could not bring themselves to do this the other bloody methods are also likely as well and freezing offers a easier way out it still is better than for example my case driving 30 min to a vet and waiting 30-45 for the vet to be avaliable.