ReadEdenPoirot, Miss Marple or a standalone? Where to start with Agatha Christie
You do not need to start at the beginning
Most Christie mysteries restore the problem and suspects within one book. Recurring detectives develop recognisable habits, but the cases rarely demand that you remember an earlier solution.
Choose Poirot for method
The Mysterious Affair at Styles introduces Hercule Poirot, but Murder on the Orient Express offers the more famous closed setting. Choose Poirot if you want the detective's reasoning to stand visibly at the centre.
Choose Miss Marple for social observation
The Murder at the Vicarage is her first full-length case. Miss Marple reads a village through patterns of behaviour, gossip and the things people assume an elderly woman will not notice.
Choose a standalone for pure pressure
And Then There Were None removes the comfort of a returning detective. Ten people arrive on an island and the structure tightens around them. It is a good beginning if you want Christie without deciding on a series.