What Turns You On?

When you choose a spanking story to read, what qualities do you look for? What kinds of spankings turn you on?  Discipline, erotic, D/s, public, fanfic? Are there certain elements of a story guaranteed to melt your heart, make you swoon with desire, or make you long to be one of the main characters? Is there a time period you like best, such as the 1800's, contemporary, or the future?  What about alternate realities? There are so so so many aspects to consider when choosing the setting and plot of a good novel vs. a short story.  A good novel will leave you with wet panties over and over, whereas a well-written short story makes you want to find your sexual partner right. this. instant. to fulfill those desires.
 I would like to know: what are some of your favorites and why?