I read a fair bit of both, but I feel that science fiction is the "better" genre.
Not that the science fiction stories are inherently better, in a narrative sense. What I mean is, science fiction allows for a much larger variety of stories, settings, themes, and characters. A greater level of unique creativity, if you will. Not to mention many of the sci-fi classics have, in one way or another, influenced the course of history and technology.
I could be biased, however. Though I read classic fantasy stories like that of Tolkien and others growing up, I was always more enamored with the works of authors like Issac Asimov, Michael Crichton, Jules Verne, Mary Shelley, H.G. Wells, Carl Sagan, Vernor Vinge, Philip K. Dick, Arthur C. Clarke, Robert C. O'Brien, and many, many others.