Good question! You will have direct patient contact in any of the fields you are considering, and as a high school senior you don't need to decide right away which one to pursue. You have narrowed it down that you want to be in the health care field and have an interest in family medicine. As far as picking which track to follow depends on a few things, one of which is certainly how long you are willing or able to stay in school before you will start working in your field. As a MD, you will be in school for 4 years of college, 4 years of medical school before you start your residency, which is where you specialize in your field. At that point, you are working with patients under the supervision of senior doctors and you are getting a paycheck. While it is not huge, it is enough to live on and if you good about budgeting you can start paying back your student loans at that point. The upside is that you will be an MD and be able to work independently. However, we are now in the era of team approach to medicine and many people find that one of the other health care practitioners such as NP or PA are very rewarding as well. To be a nurse practitioner, you need to do your 4 years of college and get your Registered Nurse degree and then do another additional certification program for the NP degree. However, if you want to start working as a nurse sooner, you can be a LPN (licensed nurse) in 2 years I believe. Physician assistant also requires 4 years of college and then advanced degree.
So at this point in your education, I think its great that you narrowed down your interests this much and I would encourage you to focus on a Pre-Med track, which will get you into any of the above programs, and try to volunteer or shadow people working in these fields so you can see what its all about and talk to guidance counselors who can guide you as to requirements for each specific school. The first few years of college will be about the same regardless of which field you choose.