BBC Sherlock, because there was an almost limitless amount of content, a lot of it was excellent, and a very substantial percentage of it was to my taste. And for the first several years that I was in the Sherlock fandom, it was also really fun. People were extremely passionate, and there was no such thing as "too weird," and the balance between "taking it seriously" and "not taking it seriously" was ideal.

Sadly that balance got lost over time, and the fandom went into decline, and things got very wanky. But for me none of that negates the years of tremendous fun I had with it.