Answer:
smart
Step-by-step explanation:
I think it is more important for the Supreme Court Justices to be smart than humble, because according to their job description, they must remain true to the Constitution.
Were the judges only humble and not smart, they might lack the judgement criteria necessary to correctly interpret the Constitution. While a complete lack of humility could prevent them from doing the best job possible, a lack of intelligence would make it almost impossible for them to perform well.