Strongest, after three expansions and several years of community interaction and feedback along with a dedicated lore team.

The stories that come with the initial package are almost always bare-bones. GW2 is great example. Sure, the racially-locked stories are decent, but by the time you choose a faction, you're tossed aside in favor of DurTreeHurneDurHur. The main character could have been from any race, and suddenly you get to clean Orr and save the world from Zhaitan with him?

... nah. Imagine the politics and racial dick-waving. How do you even write for that?

On the other hand, the Living World plot actually gets to build on the medium and uses the suspense of bi-monthly updates to keep people speculating and guessing. It took a year before they even had the first Living World introduction, and all they did was add some satellite dishes in some never-touched low-level zones.