I can't really judge a fandom on how obsessed the people I meet are, but some just stand out. For example, My Little Pony. It spreads fast, is destructive to communities, and tends to latch on to ADD/autistic creeps. I have seen their chatrooms and the deep recesses of their immense topic, and it is mind-boggling how they reiterate how "almost all bronies aren't the creepy kind." The main reason its still alive is because its latest reincarnation deliberately makes fad-friendly appearances and even references to outside media, engaging new discussion on how "revolutionary" the show is, despite that it is still stupid. It's also meme-friendly, so much in fact that websites have tried banning the constant flow of more stupid macros.
Then there is, of course, the sonic fandom, which was the main special interest-art vehicle until MLP came along. And Twilight gets annoying too.
However, I highly respect the furry fandom, for they're much more tolerant of others and don't rub in your face their stupid arguments over how amazingly perfect and justified their fandom is. They don't argue and bicker with others about their rule 34 because they don't try to shove it down your throat, and thus creating no need too. There is a long history of awesome music (see: Renard) and put a lot more effort into their art. There are also very few memes based off of them, which is a fantastic quality in my opinion.
I also don't mind the dragon fandom, but my decision is probably influenced by the fact that I am associated with it.
/opinion
