Science fiction. Hands down.
Don't get me wrong. I like the occasional sword-and-sorcery fantasy tale. I like Potter, LoTR, etc, but...well...
I'll put it this way:
My book shelf is filled with novels from Asimov, K. Dick, Crichton, Clarke, Shelley, Heinlein, Wells, Vinge, Herbert, etc, etc. The largest grouping of fantasy novels is the Potter collection.
Science fiction just captures my imagination far more than most fantasy tales, notably hard-sci-fi stories. I find more lasting entertainment from pondering the possibilities, moral quandaries, and speculative advances in technology presented in those sorts of stories.