Need a new Agatha Christie book.

So, every summer, I give myself a summer reading list. I spend weeks researching and vetting books in my genre of interest and last summer, I fell head over heels in love with the works of Agatha Christie.

This year's list has three books in it (The First Apostle by James Becker, Master and Commander by Patrick O'Brien, and Six of Crows by Leigh Bardugo), however, I would like to add another Poirot novel to my bookshelf (because I drink them like water). Here are the ones I've read so far:

1. The Murder of Roger Ackroyd – LOVED this one! Great atmosphere, memorable characters, and the ONLY one of the books whose twist I didn't see coming.
2. Murder on the Orient Express – I bought this book at the recommendation that "it might be better than you think". But I'm gonna be honest, I didn't enjoy this one SIMPLY because the ending was spoiled for me. Hard to enjoy a mystery went you know how it ends.
3. Death in the Clouds – No lie, I bought this book because one of my favorite episodes of Doctor Who is based around this one. I liked the premise, but it ended up being kind of boring.
4. The ABC Murders – Again, I liked the premise of this one…but I figured out the twist about half way through.
5. Five Little Pigs – Again, I liked the premise of this one…but I figured out the twist about half way through.

So, I've only dipped a toe into the works of Agatha Christie, but I enjoyed them enough that I would love another recommendation for the Poirot series. What's your favorite Poirot novel? I've only got enough room on the reading list for one more book, so I'm really interested in what everyone has to say. Thanks everyone.