I voted Yaoi, because I was forcibly introduced to things that involved sex with Gravitation (and the Gravitation Remixes). Before Gravitation, I wouldn't even READ anything with a pairing in it, and what I wrote had no pairings whatsoever, because romance just didn't interest me in the slightest (plus bad childhood memories, oh no). However, after having had a boyfriend and having other things happen (if you know what I mean), I've been a lot more open as far as het goes, and lately I've been going so far as to include hints of het, even if I won't write a smutfic involving them.
As far as the smut I've written, it's been exclusively yaoi of varying fandoms. I enjoy some of the mainstream couples (as mainstream as yaoi can get), and enjoy some crack pairings as well, but what I mostly love is crossovers. I would have to say that my favorite pairing of all time is Duo Maxwell (from Gundam Wing) x Harry Potter (mostly because of a fic I've started to write...). I also like catboys/catgirls, going so far as to find an excuse to cross almost everything with Loveless, or coming up with convoluted plots to give the characters cat ears and a cat tail (Rockman.exe x House wtf).
I have nothing against Het or Yuri, honestly. When I watch porn, most of the time that's what it is. However, I don't like to read about it unless it's just a minor part of the story (oh, Ron's gotten together with Hermione, yay for them, now what's this about a bad guy?) as far as het is concerned. Yuri... well, to be honest I haven't thought about reading it. There are just so few female characters that I like, and when I go to find het for them, I end up with yaoi instead. How does THAT work?
So yeah. That's a confusing and somewhat convoluted view into my mind, but I never did think linearlly anyway. Some background information for me: I'm female, 20, and quite happily engaged in a long-distance relationship with another woman. As I like to say, it's not the body that counts, but the person within it!