A fun and simple question, what is your favorite AU in either reading or writing fanfiction?

For me I have quite a few AU's I like when reading/writing, especially modern if the series I'm into is a period piece or something along those lines. I'm also very fond of high school, fantasy, sci-fi, and the occasional super hero AU. With modern/high school AU's I think it's because I find it relatable and easy to write about sometimes, and for the others I find it fun to think about what certain characters would be like in situations with magic, powers, steam punk, etc. if they aren't from a series with those settings/genres.