PLB are by far the best if you are traveling in remote locations but if you are in a relatively high visited area a whistle or other low tech devise is often the quickest for of getting help. In this circumstance i would also be more inclined to get someones attention than taking up the valuable resources of a full scale activation that a PLB would cause.

Obviously i am talking about whilst out hiking or something. It really depends on the circumstances. If i was in a plane that came down in a relatively well visited park close to town i would activate the PLB because i will want a full response from the emergency services.