I'd have to say "Inescapable," (http://brightly-lit.livejournal.com/24472.html), because it's a genre I don't usually write (action) set in a place I don't like (Vegas) with a main character who makes me kind of shudder, and it's got sex that's more graphic than I almost ever write, so it was really hard! But as a result, it was ultimately that much more satisfying.

Thanks for asking!