There's definitely major pros and cons to these. I am going through the same thing myself (should I apply for NHSC or not?).
The major pro, obviously: getting your entire medical education paid for. Can't really beat that. Another major pro: knowing you are going to be serving a population that really needs you, which is gratifying to lots of us. You also get some say in where you practice for those years, and there are a LOT of places to serve.
Cons: you're definitely going to be doing primary care for at least as many years as you take the scholarship, and if you back out, you have to pay 3x what you received (!!!).
If you're looking at NHSC, you should also look at their loan repayment programs. Not quite as much $$$ goes into your education, but at least that way you can decide after residency.
One of the DOs I know up here in Alaska did the NHSC in Nome and absolutely loved it; he even stayed on an extra year at the hospital. He was a family practice physician but worked in the ER and other "specialty" areas because there were so few docs up there. But you really have to know that's what you want to do, because there's no going back!