What could be a good conclusion for an essay on three career choices based on the thesis statement below?
Thesis: The jobs of IT manager, Air Force pilot, and combat systems officer all require quick thinking and strong problem solving skills, but Air Force pilot is the best choice due to its benefits and the researcher’s skill mix.
I'm not sure that you actually have worked out a viable thesis here. Both the pilot and the comnbat systems officer jobs require quick thinking, but an IT manager isn't working in a real time combat situation. Two of the jobs are military and have physical requirements as well as the need for visual acuity and quick reflexes; an IT manager requires neither. "Strong problem solving skills" is a bit of a cliche -- try to narrow this a bit to think about types of problems. Another question: what do you mean by benefits? In discussing careers, benefits usually mean things such as like health insurance and pension, which would be identical for pilots and combat systems officers.
Your main difficulty with the essay, I suspect, is that what you have supplied as a thesis statement is actually a conclusion. A thesis might be that X, Y, and Z are the best job for people with skills A, B, and C, and interests 1, 2, and 3, and then show that you have the requisite skills and interests and then conclude by discussing what might be the best job for you.
In the body of the essay, you may want to think about what you mean by best: most enjoyable? highest paying? best work-life balance? highest status? best opportunity to make a positive contribution to society?