It's been a while now, but Betrayal will always be a favourite of mine.
I was in a particularly angry mood when I wrote it, and in a roundabout way it vents against so many things I hated about the erotic story scene: default objectification of women and glorification of white male privilege, racism and stereotyping, gratuitous scenes of torture, shallow revenge plots, absurdly unrealistic pony training, implausible body modification, and a bunch of other stuff.
Of course, if you take it at face value, Betrayal seems to include all those elements, but I thought I did a passable job of taking each one and undermining it in a way that would make a reader see them a little differently in future.
I thought my writing crossed a quality threshold with Betrayal, but whether that's true or not I've begun to wonder. Readers certainly stayed away from it in droves. It's not exactly fun, or easy reading, but I didn't think it would be quite so alienating. Certainly, if I was recommending something for somebody new to my stories, it wouldn't be my choice. But in terms of clearing the slate so I could move on to lighter themes, it did a lot of the work.
I'm also quite fond of Pale Recluse in that it tied up some loose ends from The Doll Factory in a way I was particularly pleased with, and introduced a conflicted duo of not-quite-humans I would like to write more for one day.
I would have picked Pretenders, but due to a mix-up it hasn't been posted yet. I think it's my sexiest story.
Original Sins got the best comments I've ever had, though they got wiped in the crash. I like it, but it's not my favourite.