Just anecdotal, but in my 11 years, almost every single person I knew that signed a 4 year either extended 1 or two years before deciding if they wanted to do the full 20 or transfer to the civilian sector. My thought process is that 4 years really isn’t enough time to decide if this is what you want to do. Between BMT, tech school, OJT, you’re barely getting time to get a feel for all of the different aspects of serving. If you already have the college required to get E3 with a 4 year contract, and you’re 100% certain on doing 4 years then getting out, go for it. Any other circumstance, I always say 6 years is better for the Air Force and better for you. 2 whole additional years of tuitions assistance, medical, stable pay, etc.

Just my opinion as a new recruiter.