Use a false memory charm on a student to generate testimony framing someone else as false memory charming Draco and Hermoine.

That would fall under 5. "... find someone and give them up as Dracro's assailant/Narcissa's killer, without considering their actual guilt." And like any option that falls under that broad category, we don't know how long it would take to carry out, so it's more "Let Hermione go to Azkaban while framing Lord Jugson." (action 4 plus 5)

If I were going for the safe, boring route, I'd pick 4 combined with trying to determine (and prove) the actually guilty party who false memory charmed Hermione. There aren't very many people who;

• Are Hogwarts professors (i.e. someone who could cast the memory charm without triggering alarm).
• Have a motive.