Who are the credible characters in Arthur Conan Doyle's Hound of the Baskervilles?

As with most crime fiction, most of the characters withhold information or lie about it. What creates and resolves suspense in this sort of story is precisely the way readers are only gradually given the information needed to fully understand the events we witness. For characters:
Narrator: The third person narrator is reliable but is mainly restricted to the viewpoint of Watson and only knows or reveals information to us gradually.
Watson: He has an open and honest character and tells the truth, but is not as intellectually acute as Holmes, and does not always understand what lies behind the events he observes and records.
Holmes: The consulting detective is brilliant and seeks and discovers the truth in all of the works featuring him. At times, he will lie or engage in other forms of deception to achieve his ultimate ends, but in the end he will reveal the truth.
Sir Henry Baskerville and Dr. Mortimer: Both honest but puzzled by events.
Barrymore and Mrs. Barrymore: Lie initially to help Selden but otherwise truthful. 
Mr. Stapleton: Not credible.