Asking a bunch of literate people about the Great American Novel is an open invitation for us all to show off and make cogent, compelling arguments about the importance of [insert a favorite novel here] in the canon of American literature, regardless of whether anyone outside our small circle of literary compatriots knows of the novel or would agree. As a science fiction and fantasy writer, for example, I can make a pretty good argument for Philip K. Dick's "The Man in the High Castle" or Ray Bradbury's "Fahrenheit 451," or maybe even Mark Helprin's "Winter's Tale," and I might even get a cheering section behind the choice.
But rather than make a case for my genre, or my personal favorites otherwise, let me instead suggest that the Great American Novel is a moving target and that the space is filled by a novel that in any particular time best fulfills three main criteria:
Ubiquity: It has to be a novel that a relatively large number of Americans have read, and that a large proportion of those who haven't read it know about in other ways (for example, by a popular filmed adaptation ).
Notability: There has to be a general agreement that the novel is significant -- it has literary quality and/or is part of the cultural landscape in a way that's unquestionable (even if critically assailable).
Morality: It needs to address some unique aspect of the American experience, usually either our faults or our aspirations as a nation, with recognizable moral force (not to be confused with a happy ending).
And here we have a quandary, because novels that ring all three bells are relatively few and far between.
Books like "The Bridges of Madison County" and "The Da Vinci Code" are ubiquitous in their moment (people love them! And that's OK!) but are probably not notable over time, or seen to address the American experience in a serious way. On the other hand, novels like "Sister Carrie" or "Main Street" hit the moral and notable aspect, but no one much reads Theodore Dreiser or Sinclair Lewis anymore (sorry, guys).
In fact, at this point in the great American experiment, there's really only one place to consistently find novels that hit all three criteria: high school English class reading lists. They're on those lists because of their notability and morality; and because they're on the lists, they're ubiquitous -- a large number of Americans have read them.
Which is why, right now, the Great American Novel is "To Kill a Mockingbird" by Harper Lee, with F. Scott Fitzgerald's "The Great Gatsby" and "The Scarlet Letter" by Nathaniel Hawthorne as runners-up. Are these the best American novels? That's subjective (I vote no), but they were on the reading list when I was in high school, and now, 30 years on, when my daughter is. They are a common American experience -- one of the few we still have.
Want a different Great American Novel? Talk to a high school English teacher.