I voted for aids. What causes cancer is not entirely known. Even if we do have cure, it will keep re-appearing. But we know the source of aids. If we cure each and every aids/hiv carrier, including animals, we might eradicate aids altogether. Maybe the virus will remain dormant somewhere and reappear on contact, I don't know. But cancer atleast doesn't spread. So there is no danger of an epidemic that AIDS currently poses.