I only believe in positive reinforcement. Only an excellent trainer with a varied repertoire of training methods should use negative reinforcement only when absolutely necessary, but I am not in favor of negative reinforcement.
I found this article very interesting. It was an interview with a neurologist and trainer. It talks about the dangers of prong collars, particularly in breeds who are prone to collapsing trachea.
Tails of Seattle | Veterinary Q&A: Prong collars are safe — fact or fiction? | Seattle Times Newspaper