If you are planning on reading the whole thing for the first time, chronological order might be the best. That way you get all of the history and build your way through the epic one step at a time.

If you think you might dabble in a book or two, you'd probably want to start with the original Dune and perhaps pursue written order. As I mentioned before, the original Dune is (to me) a head and shoulders above any of the others.

Just a thought.

I can add Mario Puzzo's "The Godfather" to the books I read every few years. The blueprint for Godfather I and II, the novel is sometimes 60-ish cheesy, and even outright racist by today's standards. But overall, it's still a fine, balanced story that illustrates many aspects of the movies more diligently than the actors could.