I tend to like stories where the people having sex really shouldn't be. There can be many reasons, too closely related, married (to someone else), risk or pregnancy, public place, etc. I also like first time stories and stories where size is involved. A married couple who have average bodies, but have had 10 years of practice might be having better sex in their bedroom than two hot teens having sex for the first time under the bleachers, but it's not as much fun to read about.
