What do you think is the best ending in any work of fiction? My vote goes to Batman: The Killing Joke. To quote Tim Sale, "how cool is it that the book ends on a joke?" The Joker's concluding, and genuinely funny, joke sums up the relationship between him and the Batman, and with both of them laughing hysterically and then cutting away to leave an ambiguous ending, it really makes you wonder if Batman's just as insane as his archenemy.