Hi. I would strongly recommend that you find a prof at your school to work with in hopes that it would become a long term project (assuming you want to do research during the school year). I have done both the long term project and summer programs, and longer-term research is better by the fact that you get more done. If you want to do research in the future, this is a necessity.
I currently work at NIH, and it is a great place to work. Most of the PIs are well known, which is great in terms of recommendations. The other thing to note is that most PIs recruit freshman to work in their lab for every summer while in college, but you may be working on different projects each summer since research does not stop while you are at school. I would strongly advise you to not work in a clinical lab at NIH for the summer, since those fellowships tend to not be as good as basic science labs. You would spend the majority of your time doing paper work in the clinical lab. Another thing to consider is that it is difficult to find short term housing for summer work, and all of the options tend to be ridiculously priced for even DC.
In conclusion, I would suggest that you work with a professor over the summer in hopes to join a long term project over going to NIH. A few years down the road it may be beneficial to do a summer program for the purposes of networking, but at your age a long-term project is probably more beneficial. If you decide to do a summer program, I would recommend doing one associated with a school. It is a great opportunity for networking, and it increases your likelihood of receiving an acceptance at that particular school if the internship went well. (I am unofficially have a spot in the grad school of the place I went and I know people on the medical school admissions committee).
Good luck with your decision. PM me if you want.