Is a Snerl Human? Adventure Comics #431 (January-February, 1974)
Sheldon Mayer & Alex Toth - 8 pages
My runaway choice for the #1 spot is what I consider to be one of the finest comic book tales of all time. "Is a Snerl Human?" by Sheldon Mayer and Alex Toth (a wonderful collaboration of legends) is the back-up story to Adventure Comics #431, a book best known for containing the initial installment of the wrathful Spectre stories. It's unbelievable how Mayer and Toth can comment on the impact of mankind's cruelty and bloodlust in so few pages. This story is both touching and terrifying. I've been reading Dr. Seuss' Sneetches to my kids a lot recently, and I look forward to reading this one with them some day. They are both timeless and impactful stories. To the best of my knowledge, this has never been reprinted. That is a real shame.
I highly recommend that you check our the threads at Classic Comics at CBR. There are lots of wonderful stories selected by a group of very wise and passionate posters. I know that I now have a lot of books to track down.