The difference between the two is that citronella might be unpleasant, but it doesn't hurt. In my opinion, you don't have to cause pain to train. And, too many dogs are "one trial learners", which means that one traumatic experience may have long lasting effects. One of the pre-eminent veterinarian behaviorists in the country, Karen Overall, has taken the "against" position, and I agree with her.
http://www.hollysden.com/say-no-to-shock-collars.htm
Regional Director for Massachusetts, International Positive Dog Training Association
Director, SeniorCare Pawsitive Connections Program
AKC CGC Evaluator #3669
Therapy Dogs, Inc. Tester/Observer
Sioux, CGC, TDInc.
Maska, CGC, TDInc.
Sequoyah, CGC
Fergie, Retired Lap Dog, Age 19
Dancer, CGC, TDInc. (1989-2006) #1 Heart Dog
"If you talk to the animals they will talk with you and you will know each other. If you do not talk to them you will not know them and what you do not know, you will fear. What one fears, one destroys." - Chief Dan George
"The fidelity of a dog is a precious gift demanding no less binding moral responsibilities than the friendship of a human being. The bond with a true dog is as lasting as the ties of this earth can ever be." ~ Konrad Lorenz