At this point, I'd say The Road is probably his most famous in that more people would claim to know it, either because of the movie or because of Oprah. But I know what Mike means, and I agree that Blood Meridian is by far his best work, and probably one of the best American novels ever written (it's my favorite American novel of the 20th century). It isn't aesthetically postmodern, despite being published in 1985; it's more like a great late modern novel that missed the boat, but so accurately and terrifying captures the explosive violence that accompanied westward expansion. And it also contains one of the greatest villains in the history of literature: the Judge is a villain on a Shakespearean level.