Look at rankings with a grain of salt, first of all. I am told that the PC rankings are pretty useless.
Which is more important depends on what you want to do. If you want to go into academic medicine or do research, the research rankings are somewhat important.
Primary care is generally defined as pediatrics, general internal medicine, family medicine, and sometimes OB/GYN. At one of my interviews, the dean added psychiatry and emergency medicine to that list. When people talk about having a regular doctor (who refers them to a specialist if they need it), they mean a primary care provider.
If you are going into academic medicine (that is, you want to teach, administrate, or do research at a medical school or teaching hospital), you should consider the rankings when you make your decision. If you want to go into private practice, especially primary care and other lower-paying specialties, most people's advice is to go to the cheapest school you can get into.