I signed up for Navy HPSP knowing that I probably would not go straight through. It didn't matter because I wanted to serve in the military for a few years. Despite my current cynicism about the system as a whole, I'm still glad that I signed up and would do it again. However, I am actually grateful that FS/UMO/GMO x4 years is an option, because I was suprised that military GME is not as good as I thought it would/should be. It is with respect to the quality of military GME that I was naive.
That is not a criticism of all military physicians. The average military resident is probably more professional than the average civilian resident. The problem is that the civilians have far more patients to take care of and learn from.
My beef with the USAF is what I have seen it do to the careers of others. A medical school classmate did USAF HPSP basically to pay for school. That was a stupid decision, but he is a very smart guy -- graduated AOA. Any internal medicine residency would have interviewed him. However, he got to choose from the USAF IM programs, and he is training at a med center that is basically a glorified clinic. Therefore, the trajectory of his career dramatically changed for the worse because of AF HPSP. Again, it doesn't matter if you are AOA or have a step one of 250 -- without taking care of lots of sick, complicated patients as a resident, you will not become as good of a physician as your civilian counterparts who trained at quality civilian programs. Period.
That's where I am coming from.
Ultimately, doing four and out doesn't have to be a bad experience. Again, I am very grateful to have the option of serving my country and then moving on to civilian training. I love my patients, and ultimately I think this experience -- coupled with a solid residency -- will make me a much better physician than I otherwise would have become. Taking a few years to serve your country after internship is not necessarily a terrible experience. It is far preferrable to getting stuck with several years of poor training. Consider Dr. Oglesby Paul, former dean of Harvard Medical School whose training was interrupted for four years:
http://alumnibulletin.med.harvard.edu/bulletin/spring2008/paul.php
In sum, Army or Navy HPSP may or may not be the right choice for you. Make an informed decision. However, for the reasons cited before, I cannot understand how any informed person could sign for AF HPSP.