I had always thought Twilight Sparkle was the pony that best exemplified the spirit of epistemic rationality. If anypony should possess the truth, it must be the ones with high p (p being the letter used to represent the pony intelligence factor first proposed by Charles Spearpony and whose existence was confirmed by later psychometric research by such ponies as Arthur Jenfoal) who devote their lives to tireless scholarship!
After this year, however, I think I'm going to have to go with Applejack. Sometimes, all a pony needs to do to possess the truth is simply to stop lying.
Just—stop fucking lying!