Time to get this back on topic!
I voted other...by accident
My actual vote actually goes to fanfiction because I just have more fun reading those, I certainly have more fun writing them, especially if they are more on the silly side. In fanfics I generally prefer a kidnapping over a friendly tie up because it fits better.
When going with a regular story I prefer either sibling tie ups or best friend ones because, again they are more fun for me. An actual kidnapping without the room to make fun of things like in fanfics are a bit of a downer.
Things I'm not into are master and slave, unless one plays it up to comical degrees, Fraternity and hazings because the concepts are alien to me and stories about Celebrity because writing or reading these things about actual people makes me quite uncomfortable.
Aren't kidnappings, ransoms and maybe even hostage situation are the same thing? Or at least in the same genre.