As someone who's been in the military(US Navy) for 7 years and currently does recruiting, here's my take on it.
Some people gets a lot out of it. I'm in a much better position then I was before I joined in pretty much every way possible. I got a lot of training in a field I can use outside the military(Nuclear Power Generation), a nice bit of money saved up, almost enough college for a degree program. I know a lot of people who like the security knowing they won't be laid off and they would pretty much have to work at it. Not to mention getting to travel the world and see a bunch of interesting things on the government dime(as well as getting enough vacation time each year to do stuff on their own).
On the other hand, the government will pretty much have you on call 24/7 with the possibility of deploying you and it's hard to maintain relationships. Which makes it better to do when you're young and aren't married. You can live on the ship/in the barracks but you live under military rules if you do that. You can go on deployments from 6 months to a year dependent on branch and duty, which could take you to some really cool places or stick you in the middle of a desert getting shot at.
What's important is to realize why you want to do it:
Is this something you want to do or something you feel like you have to do?
Do you understand what life in the military is like(and not from watching movies. Very few movies actually get anything related to the military right)?
Are you ready to commit to a contract of 4-6 years? Which means once you start, you keep going until you're done. The moment you tell a recruiter you want to do this, you had better mean it. There are ways to get out of the military before your contract is up but they don't help you in the long run(Smoking dope, but you'll be flagged forever for getting kicked out on a drug charge).
Are you within military physical standards? Is working out part of your life right now? Boot camp will get you in shape but you have to be within standards before you can even get on the plane and your life will be hell in boot camp if you can't pass the fitness test when you get there.
Have you taken the ASVAB? It's the test they judge what jobs you qualify for from. Recruiters will give you a practice test in their office to see if you are smart enough. If you don't pass, they'll send you out the door. If you get a high score, you have a much better chance of getting what you want as far as a job(all the jobs with bonuses require a high score).
Just because you qualify for a job doesn't mean you'll get it. Just because it's available a week before you go to join doesn't mean it will available when you go to join. Be extremely wary if a recruiter says they can guarantee you a particular job before you go down to join. Some branches can do it on your contract but none of them will do it from their office.
And pretty much all the branches want you to go down to join the branch, not a particular job. If you only want one job, a lot of recruiter will show you the door.
Also, regarding branches...
In general, Navy and Air Force have more high tech jobs then army and marines.
Not all Navy jobs go to sea. A lot of Marines do go to sea(the Navy and Marines work closely together).
Every branch has jobs relating to aircraft, with the Air Force and Navy having the most and the Marines and Army having less so. Also, every branch has their own aircraft(this is a pet peeve for me because I'm tired of people telling me that the air force flies planes off of aircraft carriers).
Very few jobs in any branch involve flying in a plane/helicopter. Most of the airforce stays on the ground. It's really, really hard to become a pilot, so don't ask unless you have a BA/BS with a really high GPA. Be extremely wary if a recruiter tells you you'll be flying an aircraft anytime soon(maybe flying in one if you specially get an aircrew job).
A word about recruiters:
1. Be honest with them from the beginning. Lying to the recruiters just makes everyone life more difficult. If you aren't qualified, they will tell you immediately and if there is anything you can do. If you aren't qualified, going to another office for the same branch doesn't help. Even going to a different branch probably won't help.
2. Recruiters are required follow up people likely to join, so don't be surprised if they call you later asking if you are still interested. They will continue to do this unless you are not qualified or you tell them you don't want to join. If you really don't want to join, just tell them. They aren't allowed to assume "No contact/Won't answer the phone"="not interested". On a similar note, don't set an appointment then not show up. It's extremely rude, wastes their time and they will not be happy if they ever see you again. Reschedule or cancel if you can't make it.
3. Recruiters talk to other recruiters, so if you piss them off, you may find yourself blacklisted from one branch or possibly all of them.
4. If you talk to all the branches and then choose one, man up and tell the others you're not joining with them when they call. They should leave you alone at that point.
Finally, just to make sure you don't waste your time.....
-If you're taking prescription meds(ADD/ADHD, anti-depressents, anti-anxiety) or have in the last few years, don't bother. You have to be off them and stable to be medically eligible.
-The army won't take you if you have any kind of drug/alcohol related legal issues(MIP, DUI).
-The air force will run a credit check on you, so if you have something in collections, don't bother.
-The coast guard requires a 75 ASVAB, no criminal/legal/civil issues in your past at all(this includes speeding tickets) and no body fat exceptions for being overweight. If you do get in, be prepared to wait 2 years to go to boot camp from the time you sign up.
-None of the Branches will take felonies. Even minor ones.
-If you have a GED, don't bother unless you picked up some college credits. Most of the branches won't bother to talk to you.
