I like well-written AUs, but they are hard to come by. That is because, as I had to find out, they are hard to write. With AUs more than with any other kind of fanfic, imho, you have to at the same time leave canon behind and explore different avenues, and yet stay true to it enough so it's all plausible, all believable to the reader in the verse you are writing. And that is really hard to do. I keep trying, because I love the challenge.