Suchet's Poirot is definitely good, but I should point out that it is produced by ITV not BBC (their long term rival). My mother used to watch it, so I'm very familiar with it thanks to her.

However, I've never been much enamoured with the Miss Marple adaptations. Joan Hickson's is maybe the best (even though I prefer Geraldine McEwan as an actress) but I never took to it like Poirot.

You might like the nineties Jeeves and Wooster which stars Stephen Fry as Jeeves and Hugh Laurie (of House fame) as Bertie Wooster. It is formulaic but fun. I think it's the best thing Stephen Fry ever did.