Its a bit tricky I think to Judge for me because the thing that makes the DRK quest special, beyond it being well written, is that it is very personal to the WoL in a way no other quest is and is the biggest insight and development for the most important character in the story.

That is why I think it get harder to judge when you add in more qualities. Quests like the MNK quest are very lore rich and get delve into the history and story of Ala Mhigo and in that sense they offer a lot more details on the story of the world. SAM offers a very interesting counterpoint to the overall theme of violent revolution in SB where it argues that such revolution isn't always the best path to change. Some of the Postmoogle quests, while short, are endearing stories like the Keeper who's sister has turned to banditry after being discriminated against. Some of the sidequest chains in HW and SB are very good too giving insight into the issues of culture or personal stories about the people living in the areas.

DRK is amazing though.