Take my advice with a grain of salt, since I'm no longer on active duty.
I'm not familiar with Army or Navy aviation, I was one of the few C-130 guys who didn't go through the Navy flight program down at Corpus.
The Air Force is a terrific way of life. Not all my time in the AF was spent as a pilot, only about 3/4 of the time, but I loved my time and wouldn't trade it for anything.
UPT will be the hardest year of your life. As a student, you're under constant scrutiny, constantly being evaluated, tested and stressed. You'll study constantly, subject to fear, ridicule and berating. It's not for everyone, and plenty of very well-qualified, smart and ambitious people never make it through. It's a "cooperate to graduate" system, but there are a few guys who try to slide through. They're usually found out pretty quickly.
However, the year at UPT was one of the best years of my life. The training is amazing, you learn to parachute, basic survival, how to fly high performance aircraft and how to lead. An absolutely amazing year. And it continues after UPT, there's survival school, resistance training (think how to deal with being captured and put in a POW prison), and then your follow-on aircraft training. All the while being paid quite well.
The days of big time flying are coming to an end though. With sequester, the guys in my old unit are flying about 5 hours per month. After sequester, it may not get much better as the Air Force is in a huge fuel-conservation mode, and a lot of training will be done in simulators. Missions will obviously be conducted in the actual aircraft, but checkrides and proficiency sorties will be conducted in a full-motion simulator. The new simulators are amazing, giving a full range of motion and excellent visuals, but theyre still simulators. I envision guys going through UPT now will be hard pressed to reach ATP minimums by the time their first commitment is up.
But, don't let me be a Debby Downer. It's still an amazing career, a worthwhile and honorable career and one I'd never, ever regret having.
Good luck in your decision, it's an amazing time to be a young pilot.