From an idealistic point of view you can say that a job that involves helping others is the best.
This would include Rebbi, Rosh Yeshiva, Doctor, Medical Researcher, EMT, Firefighter, etc.
An ideal job for most people would be one where they enjoy the work and make a decent living while doing it.
Below are a few points that I think should be considered when looking into a career.
a) What you absolutely need in a job:
1) A means to support your family.
b) What you need to know about yourself:
1) Do you prefer working with your hands (contractor, electrician, plumber, etc.), your mind (accounting, data processing, law, etc.) or both (medical field, science).
3) Are you ambitious career-wise, or are you content to go with the flow?
4) Is the relative security of a government job and pension something that appeals to you?
5) Be realistic in your expectations. Not everyone can be a billionaire hedge fund manager.
c) What you should do shortly after leaving high school:
1) Take an aptitude test. Get an idea of where your talents lie and what jobs may fit them. Know what schooling is needed for different careers.
d) Job security: