7. The Wealth Of The Source
Throughout the history of the Batman run, the Joker has appeared in some of the consistently best story arcs, adding an extra element to those stories that even the most famous of his fellow villains fail to inspire. Every time the Joker returns now it is heralded as an event, rather than just another story, and that has a lot to do with the past successes his appearances have seen. If the script-writers were to return to the source for inspiration, and an appropriately grand story to celebrate his return, they will find classics like Wildcard, which would explain his return in response to a copy-cat, or Soft targets which could take the Gotham PD angle more, and allow for a second or third act appearance of Batman or the Killing Joke, which could offer some insight into his origin (more of which later). Personally, I would suggest that either The Clown At Midnight or Arkham Asylum would represent the best opportunities to bring the character back, or a slightly rewritten version of A Death In The Family that would see the death of Joseph Gordon-Levitt's Blake used as the catalyst for Batman's own return.