I wouldn't say that the air force is the most competitive branch, they are probably all about the same unless you try to get into special programs like special forces, nuclear power, or diving. Did a recruiter tell you that?

Even when times are tough, the up-or-out promotion system in the military means that they keep the pipeline flowing, so someone who has some college and wants to enlist should have a pretty good opportunity. This assumes you can pass the medical and have no criminal history.

Before joining the military consider ALL branches and what you want to get out of it: a short-term job, excitement, a career, job skills for the civilian world, travel, etc.

Then pick the branch that can best guarantee that you will at least get to try out for a job you want to do. Don't forget the coast guard.