Along with BadApple, I am also currently stationed at Kunsan AB, South Korea. I have been active duty for almost 16 Years and if I retire at 20 years I to will be 38 years old collecting a paycheck for life. My last base I worked side by side with and Active Reserve Unit. These guys and gals, mostly were active duty, did their 4-6 years then crossed over to reserve. Nothing against it, but that can mess up retirement plans if you dont plan correctly. If you are 20 years old, and go traditional Reserve, (one weekend a month, 2 weeks a year, deployment once inawhile) you will need to work almost 35 years untill you are able to retire. Not to mention in the reserve E-1 thru E-6 come fairly quick, or can be. Not uncommon for a guy in to be in 6-7 years and be an E-6. After that you need to apply for certain job titles.
Cons of Active Duty:
Depending on job, lots of deployments (can be a Pro also)
Dorm life if you are single (untill E4 roughly)
Lots of moving, base to base (can be a Pro also)
Working some weekends, holidays, long hours, etc
Getting paid less then minimun wage
Pros of Active Duty:
Deployments (tax free!!)
30 days a year PAID vacation!
College credits for dang near everything
Seeing the world!
Serving your great nation!
Medical and Dental for free, from day 1 (in the reserve you have to be on "Active orders" to get medical care)
And I'm sure there are a ton more
Either way, just weigh your options and choose what you think is best, if you go active do the 4 years, if you life it, re-up if not then go to the reserve. Also, Thank you for atleast thinking about serving your country!
BTW My job in Korea is in the Safety office, and I shoot birds/deer and get paid for it.... Just saying.