The Prior service program is one of the Air Force’s most selective programs. We often have prior Army, Navy and Marines that go years without jobs. Even though they have all passing PAST tests. The Air Force’s priority is new enlisted for pipeline slots, then maybe backfill with AFR or ANG students, and then finally Prior Service. So I would really recommend not going in the Army in general, and just go straight in for PJ if that is what you ultimately want to do. The reason I say this is because there really is not a career field you can go into that is going to make you more prepared, PJs need to be good at all of that stuff including the medical and "ground pounder" aspects of the job. Additionally, you can still attend classes or just do online classes while you are in the Air Force. The biggest advantage you will gain from being in the Army is an appreciation for the Air Force to be honest.   

I have worked with both, and if you want to see more action as far as combat is concerned then I would recommend going the ranger route. IDMTs definitely get lots more medical training though, so if you are looking for that then go for it. Another thing to consider is that being in the Army compared to AF is a different beast, you will be treated much more like an adult in the AF. Just my 2 cents.