As much as I love Party Of One, I'm actually kind of happy about the tie. Both episodes are top tier. Sure, I think Party is way better, but that's the fanbase for you. And it's a great thing!
I feel that MLP: FiM is one of the hardest series to actually rank in terms of episodes. They are all pretty much amazing. But in this case, I had to go with Party Of One. It's epic.
I get the feeling that as soon as Season 2 begins, Discord will become the de-facto troll for the fandom. Or at the very least, the co-troll. The co-king of trolls.