With Pandaria I highly advise completing every zone to the end. It's generally worth it for some of the story arcs. The Jade Forest for me was one of the most moving in the game. At the end of it I found myself just staring at the screen for five minutes. Valley of the Four Winds is combo'd with Krasarang Wilds so you have to do both to get the end of the story.
Kun-Lai doesn't have much of a story, but there's some interesting stuff going on that's worth seeing but it's a little confusing near the end as the story rounds up with an instance unlike the previous two/three zones.
Townlong Steppes should be followed on after completing said instance (Shado-Pan Monastery). Fun with a nice climactic fight and leads directly in to the Dread Wastes where you get to meet the Klaaxi. The Klaaxi are fun.