best: Silent Ponyville, it's a Silent Hill/MLP crossover. Really well-written, to the point where the author even wrote up different endings for each story (two complete so far, one focusing on Pinkie and one on Fluttershy)
saddest: don't really have one since I usually don't read sadfics, but Silent Ponyville has some sad scenes in it, fittingly enough
scariest: since creepypastas based on something count I'm gonna have to say Ben...that shit still creeps me out
worst: cupcakes, I just found it to be meh..it tried to hard and became a parody of itself