I think Murder at the Vicarage and The Moving Finger' are the most humorous, followed by The Murder of Roger Ackroyd. For a book club, T M F..the best as compact. For admiring her work at leisure: 'Death on the Nile' is a tour de force of characterisation. I prefer it's representation of love to Shakespeare's ' Romeo and Juliet' - although, arguably, his tale wasn't meant to be a focus on love - more a rebuke to spoilt youth. She refers to R and J too, when writing about a character - it might have been the young woman in 'Five Little Pigs'.
I am such a fan. I think that Christie sees deep into human nature and recognises psychological patterns. I mostly like the fact that she is right a lot: SPOILER alert - the character of Pat on Pocket Full of Rye, for instance who the villain falls in love with, is you feel the type a sociopath would fall in love with. She also saw that a lot of these sociopaths did have 'good war' as did the baddy in 'Taken at the Flood' ( an indifferent work.)
I believe she must be inspired by one incident, one occasion, and that sets her of on her writing spree. There's the sense that she understands that incident and that person entirely. It must have been tough for her, as she understands evil thoroughly, as well as good. I see her as a moralist, too.
Hers is an unusual viewpoint, in todays's era, where it's just about true to say that the social model of crime is still the one which underpins society's reactions to morality. AC believed in the sociopath, I think; the evil, schemer and charmer, and she sometimes seems to be warning that we should be aware that that dangerous kind of criminal does exist.