The choice is totally dependant on the submissive that is being trained.Usually a combination of the two is a better tack. Each person is different and a good dom needs to be aware of how his sub will act. This will then help to determine the intensity and depth of both types of training.

My slave is a very strong and willfull one. And a painslut to boot. I use both types for her, although the pain punishment is done with an Austrailian tail, something she does not like at all. Other subs can be delt with a harsh word or just a look, it again, depends on the person you are dealing with.