It's not all me - I have my favorites (like "a day in hell") which nobody else seems to like as much as I do - so they don't stay featured. Generally, I feature the highest rated stories in each category - I read them first to make sure that they didn't get around the ratings though, and it really comes down to my decision on a tie. That happens rarely.
I wish that the way they presented on the featured list was by rating though, rather than by letter. Oh, the other thing I do is allow others to make suggestions for stories to be featured. Contact me by PM if you feel one should be featured.
march