I think "Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo" is probably one of the greatest sentences. As it shows how completely ridiculous our language can be, as well as how flexible it can be. Also, it's always fun to see. There isn't anything deep about the meaning, but it's the lexical complexity of it that makes it nice. If you go by meaning, then you can accomplish the same meaning in a different language. Which IMO doesn't really make it the best sentence of the language. The meaning might be great, and hell, it might be the best meaning in any language. But it still doesn't show off the language in it's full or give it a reason to be the best in a particular language (is it the best in a different language as well?). So had the question be "What's the single greatest sentence ever written?" my answer would probably be different. But in the english language specifically, I'd have to go with the buffalo sentence.