I think positive reinforcement should be used whenever possible.
I don't like the shock idea, and would never do it. There are other ways to correct without resorting to imposing physical discomfort. I have resorted to the barker breaker (a corrective beep, not on the collar) and the citronella collar to stop barking. They both worked. I still wonder, however, if there was something positive I could have done instead.
