For a four-year degree, I would say Engineering followed by Nursing.
Engineers can make six figures if they're talented, work hard, and have reserves of ambition.
Charge Nurses can make $60k with 36 hour workweeks in larger hospitals.
For a higher-level degree, I would stick with the traditional Medicine or Law, although I would say that Medicine will be much more "stable" when it comes to a weekly paycheck.