I will pick Philip Jose Farmer's
Riverworld and Other Stories.
Put it in Short story/anthology.
It is the original story which would eventually become the series of novels that start with "To Your Scattered Bodies Go"
In brief, every person who has ever lived on earth from 1000000 BC to the 21st century have been re born on a planet made up almost entirely of a river that flows all over its' surface.
There are 10 other short stories in this book.
They were written between 1968 and 1979. I enjoyed the Riverworld novels first, but was thrilled to go back and read this also.