Teufelhunden,
With your prior service, and therefore the years in service pay increase, you'd be crazy to pursue a full deferment and live on civilian residency salary vs. Navy pay.
Regardless of your long term specialty choice, you're going to match in an internship only out of med-school, so this makes picking a little easier. You should have a good idea if you are an internist vs. psych vs. surgery type, and that can guide the internship choice. If you're undecided between specialties, and are looking at say medicine vs. radiology, you can always match for an internship in medicine and decide later, you need the clinical base year anyway if you choose rads.
You do get priority for straight through training if you're prior service, for the reasons you stated as well as the fact that you've paid more dues to the military than others. It's not a huge plus factor, though, and it won't trump someone's GMO tour if you haven't had one.
Historically, here's the breakdown of specialties and likelihood of getting straight through.
Almost certain - Medicine, Psych, OB-GYN, FP
Highly variable, possible - Peds, ENT (2 interns my year)
No Chance - Gen Surgery, Ortho, Ophtho, Derm, Radiology, Emergency Medcine, Anesthesiology.
Remember, though, if you do staight medicine, you'll almost certainly need to go out and do a utilization tour as a general internist before coming back for fellowship. Those who did come back from GMO land would have priority over those with no fleet time.
Things do change. My year, 4 of my fellow transitional interns walked into anesthesia spots because it wasn't popular 4 years ago...it sure is now
Finally, don't look at the GMO tour as necessarily bad. The non-Dive or Flight spots are only 2 years, there are even a few single year GMO spots overseas (unaccompanied). I'm very thankful for my tour. I could have trained straight through in anesthesiology, I said no and went Dive, have had a great time and am going back for Radiology after a lot of time to think about what I really want to do. I'm much better off for the tour, though I can understand your situation, I'll be 32 not 38 when I go back. Hope this helps,
DD