What a great debate Simon. I used to love reading Agatha Christie novels when I was young but can’t recall the Roger Acroyd one at all so will give that a read. The person that most matched my impression of Poirot was Albert Finney’s portrayal. I didn’t mind Ustinov but like you I am on the fence with Brannagh. As for Miss Marple there is surely only one candidate; Maragaret Rutherford!