Sherlock fandom:As crazy as they are intelligent, they have to face a lot of prejudice against them, but usually don't care. The fans suffer from extreme boredom (due to the ridiculously long hiatuses) and do anything to cure it. Observant (and dedicated) as they are, there is barely a detail in the show that hasn't been found, pointed out and analysed to hell and back yet. Most of the fandom is made up of intellectual elitists who think they are better than anyone else (the Sherlocks) and more easy-going people who know how to turn everything into a witty joke and are a bit pervy, like John "Three Continents" Watson.
Doctor Who fandom:Goes from loving everything and everyone to pure spite and aggression so fast it will make your head spin. But overall, it's a fandom with a big, big heart that shares a lot of dramatic emotions from happiness to grief, always watches out for the little things, embraces what it is taught, is full of curiosity and has a weird sense humour.
Supernatural fandom:Basically one big, dysfunctional family, like the Winchesters. Deeply emotional, similar to the DW fandom, but this one focusses more on grief, disappointment, despair, anger, hatred and fear, often resulting in painful fights when emotion and personal attachment cloud the fans' sense of rational judgement and even their dark humour doesn't help any longer. Still a surprisingly educated, creative and dedicated fandom, with people that will spill out their heart for what they love, and a family that sticks together throughout all the pain.