I've never given any thought to what might be the best poem ever written in the English language, but Sven Birkets, in an essay reprinted in The Story About the Story, edited by J. C. Hallman, considers a worthy contender: "To Autumn" by John Keats. As Birkets writes, "I have seen it cited many times as the most perfect poem in the language. A more suitable test case for beauty, it seems, would be hard to find."