Wow... You put both Sci-Fi and Fantasy on there...
I'll give my reasoning for Sci-Fi here: Because it's got a vast scope with actual explanations for things, and in an intelligent mind it all seems plausible. I'm all about figuring out how something would happen. Even in fantasy, I'm the one drawing elf skulls and wyrm vertebra and wyvern feathers, writing about how to set water on fie magically, etc etc. Sci-Fi cuts my work out for me.
It can apply to steampunk, dystopian, and genetics. It's all science.
Every TV show I watch is either geeky or Sci-Fi. Eureka(canceled), Firefly(canceled) and Mythbusters. I'm heavily considering watching some Dr. Who, but my schedule will not allow it. I haven't even watched Mythbusters in weeks. But you get the idea--it's one of my favorite genres.
I'm a certified GEEK and I kind of have to... It's in my blood to love science, and I must say I really don't like modern, basic stories or mysteries. Straying from that, Sci_Fi is a fabulous genre that easily takes the cake. Which is not a lie, it was there, and how could I lie about this?
Yes, my video games are Sci-Fi, too, aside from Zelda. And I RP in Sci-Fi, I'm modding one of two Sci-Fi Rps ever on this site.
But I chose fantasy, because it's easier to find fantasy novels that are geared towards young adults and I can't resist dragons.
I STILL LIKE SCI-FI BETTER.