The best in terms of my personal experience were Touhou Project and BSD itself. BSD fandom is much more tolerable if you stay out of the big ship spaces. People talk about other things and characters, with characterizations I agree more lmao. I didn't get to befriend people in the Touhou fandom, my enjoyment of it came from the loads upon loads of fanworks.

Worst was probably Naruto in its heyday? I think. Honorable mention to RWBY, which I wanted so badly to get into and the fandom's infamy deterred me from that.