Yes, and I think they're both ingenious in different ways, Mona! Frankly, I find
And Then There Were None contrived because she was trying to fit the plot to the verse. Apparently she admitted that it was the hardest one to write, although I'm sure she enjoyed the process of plotting it.
I still say
Ackroyd is my favorite, although it is more accurate to say it's only one of my favorites.
Five Little Pigs,
The ABC Murders and
Cat Among the Pigeons are a few others I can think of besides
Death on the Nile and
4:50 from Paddington.