First of all, you are awesome for offering to write whichever of the fandoms we got matched on! This is my favorite time of year and I will be thrilled with whatever you decide to write! Now, on to the fun stuff.
I don't have much more elaborating to do beyond what I said in the actual details box on the sign-ups, so I thought I'd give you a few generalized likes and dislikes!
I like horror, particularly Lovecraftian style. I dig mysteries, too, the twistier the better. Romance is fine, and I kind of prefer it to outright sex. Don't get me wrong, I am not opposed to some porn, but that kind of depends on the fandom. For example, please don't write Adventure Time smut. That would weird me out in a big way. I'm pretty open to any sort of story, though, and there's not a whole lot that I dislike.
Really, the only things that I object to in fics are character death. I tend to like my fic to have a happy ending, or if it's a more open-ended sort of story, I like it to end on a positive note. I'm not a huge fan of angst unless it's resolved, but other than that I'm good for anything!