My favorite that I posted in the other thread is Chapter 31 of Song for the Undead:
http://absolutechaos.net/viewstory.php?sid=9551&chapter=31This was the first chapter that the "undead," a.k.a. zombies, were introduced, so it was a big part. Up until that point, we had even posted the story under a different title so as not to spoil the moment where the dead came back to life, cause it was meant to be a shocker. So not only is it a major plot point in the story, but the anticipation had built up so much in Rose and me that I really needed to do it justice and get it just right. And I think I did; it came out exactly as I had imagined it in my mind. It's only been about a year since I wrote that part, so it wasn't that long ago, but still, I reread that chapter the other night when I posted the link for Mare, and there was nothing in it that made me cringe, nothing I would want to change.
The one that always comes to mind for "hardest" is when I chopped off Nick's leg in Broken. Starting with Chapter 106:
http://absolutechaos.net/viewstory.php?sid=5354&chapter=106That one in particular I remember being really hard to write. Again, I had built it up so much in my mind, but it wasn't just about doing it justice; I was kind of nervous about doing it at all. At the time, it seemed to me like OMG the worst thing I could ever do to Nick in a fanfic (even though I'd killed the poor guy off before; go figure LOL). I don't really feel that way anymore, but it did really kinda freak me out for awhile, and I was worried about the reaction and worried about my ability to write the rest of the story after that, and blah blah blah. It turned out to be the best move I could have made for the story, I think, and my favorite section of Broken is that last third of the story, post-choppage LOL. Maybe because it was such a challenge to write.
Sorry, I'm really long-winded. LOL