Dune is more profound, but as far as predictability goes, it's almost a one-way street as a book. Which is not to detract that it is very good, and that Stranger in a Strange Land is similar, once the "church" is formed. I found SiaSL as giving interesting insights into what a completely weird alien species might be (much like Asimov's The God Themselves, a personal favourite.) I think that since these two are good, classic books picking one over the other is just a matter of preference, although Dune will be in far more antologies and SiaSL will be more an underdog. Do you have any SciFi recommendation, by the way?

My favorite work of science fiction is the Hyperion Cantos by Dan Simmons, I think it's really an unmatched tour de force in the genre.