almost 2 years ago - PDX-Trinexx - Direct link
Depends on where you're playing for the most part. Northern Lords and Fate of Iberia are fantastic if you play as a Norse or Iberian ruler respectively, but since those are regional flavor packs you won't get much out of them if you're playing somewhere else.

Royal Court and Friends & Foes are region agnostic and apply to the entire game, however.