Personally, I would like to do research that would be able to help people make drug molecules for lots of different illnesses. There are so many terrible illnesses that choosing one to cure is impossible for me. I do think it is important to come up with cheaper treatments for diseases too, so that diseases such as Malaria and ones that affect the poorest countries can be cured.
I would love to cure any disease as in my opinion they are all worthy of treatment. In reality though we have to see the work we do ourselves as being part of a much bigger question and that we fit into a small part. That other people are contributing to answers the question helps a cure to be developed