I am going through coursera's startup engineering course and can't decide what to focus on for my final project: A medical startup, unsexy, but looks likes it

I am going through coursera's startup engineering course and can't decide what to focus on for my final project: A medical startup, unsexy, but looks likes it could be very, very profitable. I have no domain knowledge for about half of this idea, but I have an experience Doc who can cover that part, and is excited about the possibilities. An educational startup, something very close to my heart, where I have a lot of domain knowledge and experience. I also think I have struck upon a rock solid business model that can make me money (think lifestyle business, but a little higher) yet allows me to create a business that I would be very ethically proud of.