Hope you have a cup of tea at the ready (a proper one in a cup and saucer) when watching this. Joan Hickson's Miss Marple always seems to have a cup of tea at some point in each episode.
I think Joan Hickson as Marple, David Suchet as Poirot and Jeremy Brett as Holmes did a superb job and would be hard to beat. Joan Hickson is the best Miss Marple for me too. Julia McKenzie is OK but I never liked Geraldine McEwan in the role, maybe because I'd seen her play a sadistic nun in the Magdalene Sisters.