its kinda tough mentally and physically but more mental. Army is probably the only one that will give you the choices you want. expect about a third to half to quit before the class is half over - you could be one of them. have a plan B. you should have seen that special they had on tv a few months ago about marine ocs. those sergeants they had running things were pretty sharp but army tac officers are on another level because they are way smarter, mentally quicker, younger, and less forgiving. even so, the marine ocs story showed some pretty cut up and smart guys bailing after beginning to question themselves. its been 40 years ago that I did it at 19. I still can't explain what they did to us. we went in college drop outs/high school grad jackasses and came out the other end chock full of initiative and barking orders. it was pretty much the formative experience of my life. I've been back a time or two, inducted into the hall of fame, and pulled together my class for an internet reunion. It is good experience, especially if you can still get into the war and practice your new trade. What I learned then and the many mistakes i made and learned from put me way ahead when it came to leading people later in my late 30's and beyond. its a great training ground for the rest of your life but you have to really want it. you gotta be able to do pushups till they get tired of watching you. you got to exude enthusiasm squared for every little thing they tell you to do. you have to find those times and places to show initiative and then have the nerve to do it and not fold when they jump on you - moral courage is everything.
Most likely it will be the toughest thing you ever do and the first big no sh#t challenge of your life. If you are not decisive and confident, try something else. All of my classmates had great careers in their chosen fields. Some of them are just names on a wall now. Take stock of yourself and if you can't decide in 10 minutes its not for you.