Both are fascinating, and really quite similar if you think about it. I just happen to have come across more fantasy books that I enjoy reading, but not so much look with sci-fi. Writing, on the other hand, there are simply too many possibilities with both genres, because magic has rules and limitations just like technology does, and technology can be so advanced as to seem like magic. Lots of fun to play with both, especially when alien species or fantastical beasts are concerned.
Science fiction, specifically because it requires more of the creator. Even if the science is BS, there has to at least be an internal logic to it that can be followed. There are ideas beyond what is being depicted. It's deeper.
I surpose I enjoy what imaginations and ideas humans had in the past, it is much mure surreal, mysterious and interesting than what ideas we may have for the furture. I easily understand peoples interest in sci-fy, but I'm just more into the never-existing ideas.