Well, I once had a similar situation, but it was Navy v. Marine as opposed to Air Force. With about three days left until I had to make my decision, I started freaking out. Until that time I was 95% sure I wanted to go the Navy route, but the closer the hour for decision came the more unsure I was. I got two great pieces of advice. The first was this: "Joining a service is a lot like getting married. You have got to love what you are doing, or else you will be miserable, because like a wife, it will take a lot from you." The second was that the decision ought to be about culture-fit. Every service has a different culture. I know people who have flown with the Air Force, the Navy, and the Marines. All have been good people. When I thought about it, the peopel that I respected the most were Marines, and a lot of aspects of the Marine Corps seemed to be more in keeping with my own attitudes and ideas.
As a Marine SNA, I am convinced that the greatest thing I could do in life is to put ordnance on target for a Grunt on the deck, or CASEVAC a wounded Marine so that he/she can go home again. After all, it's not about you. It's about the Pfc's and LCpl's on the ground with an M-16 and 120 rounds of 5.56. In the Air Force, I beilieve that it really is about the pilots. After all, it is the reason that the whole organization exists. The Navy strikes me as a bit of a middle ground between the two. Naval aviation is a very distinct community but they recognize that they are part of a larger team.
Probably one of the biggest differences between all of the services is what you will be doing when you are not flying. From what I've been told, and I'm not saying this is accurate, if you are a pilot in the Air Force you will spend a greater part of your career in the cockpit. As a Marine, you might be a forward air controller calling close air support, or an exchange pilot with another country. You might spend the later years of your career doing something unrelated to aviation at all. Same with the Navy. I think you will only be in a flying status for about 50% of your first 12 years in or so. Again, I'm not sure how valid any of that is, as it's mainly from old career progression charts, heresay, and my perceptions.
Bottom line: Talk to as many people from different services as you can, consider what each one offers, and decide where you think you will fit in better. Good luck with your decision and your pursuit of your dream.