Residency training is probably going to be similar military vs civilian. Ironically, military residency is probably a bit more relaxed and easy going. On the civilian side, numbers of patients matter more so. The attendings need to be busy and thus, as a resident you will be busy. This can be both a good and bad thing. It's always good to get experience. But after your 300th ureteroscopy for stones, it can be annoying having to cover that Friday afternoon 5pm ureteroscopy, yet again.
The big difference is once you get out. The military owns you in every sense of that word. They decide where you practice, how long you will be in a location, where you move to after that, etc. There is very little concern for the new graduate. You will likely be placed in one of the less desirable locations and find yourself doing very little. You'll have outpatient surgery, and most minor cases. That's great if that's all you want to do. But, if you want to do some oncology, robotics, etc, it can be very difficult to find those cases or be at a command that supports that work. Thus, in many ways the hospital will dictate even how you practice. Oh you want to do urodynamics on that patient with voiding dysfunction. Sorry, we don't have the funding for a urodynamic machine. Send out the patient. You want to do a PCNL? Oh, sorry, we don't have IR support. Send out the patient. The list goes on...
Now, if you compare yourselves to a civilian grad who comes out, he or she can probably find a job in a general region of the US. He might not get that job in Manhattan, but there's probably a job in Westchester, NJ, Long Island, or CT. So, at least he is in the general vicinity. The civilian grad will make more money - a lot more. And finally, she'll probably be at a hospital that supports her and doesn't find ways to impede patient care.
Think long and hard before signing that HPSP contract. I owe 4 years after residency. I went to a private med school and saved somewhere around $200k in student loan debt by taking the hpsp. If you take my base pay, bah, vsp, asp, isp x 3 years, board cert pay for about 2 years I am probably grossing about $700000 for the 4 years. That's just a guestimate, but I can't imagine I'm grossing more than that over the 4 years. Anyway, my civilian colleagues are bringing in at the minimum $400k per year. I know of some who make twice that. It doesn't take long to pay back all that student loan debt, squirrel away a bunch of money for retirement, and never have to deploy as a civilian doc.
Think long and hard about HPSP if you desire to become a surgical specialist, radiologist, anesthesiologist, etc. If you're going to be a family doc or internist, the argument probably favors military med.