I'd have to say Applebuck season. Thinking about the other episodes, with the exception of Feeling Pinkie Keen, it helps to know a bit about the ponies involved (whether it's twilight's obsessiveness, or fluttershy's love of animals). Both Applebuck season and Feeling Pinkie Keen are fairly self contained, and I'd even go so far as to say you learn what the focus of each episode is fairly quickly in the episode. As for why Applebuck season? Beyond the other reasons presented here (and they probably make more sense than I do at the moment), you can also sympathize a bit I think with Applejack and monsterous workloads. Such is my two cents.