I too was interested in the Air Force HPSP scholarship, but when I was accepted to the USUHS (Army), I withdrew from the Air Force HPSP. The Army has more specialties to choose from and also has more positions available. I have read that there are fewer opportunities in the Air Force for ER doctors and surgeons, however, probably the best source would be for you to have the recruiter or someone else get you in touch with a military physician who is in the Air Force, they would be the best ones to give you the details.
Also, if you type in HPSP in a search in the main SDN forum, you should get quite a few hits where the scholarship is discussed, and I remember reading a few who talked about the Air Force.
If you are more interested in the quality of life, then I think the Air Force is better in that regard. Whatever you decide, I think the HPSP is a great deal and I would take 4 years of payback as a military physician in trade for a full ride, plus $1000 a month any day.