In both the standard and colloquial sense of "epic," it would be The Stand. I read somewhere that Mr. King wanted to do a version of The Odyssey with The Stand (and I think he did), so that would be "epic" practically by definition.
And if this gets me expelled from the site and from SKFandom, with my tail between my legs and slouching toward Bethlehem to be reborn, then so be it. In his lovely book On Writing, Mr. King advises us to be scrupulously honest, so I will: I did not like It.