Having done nearly 100 technical interviews (with multiple questions each), the bug squash question gave us the biggest signal on candidates. Our question was

Having done nearly 100 technical interviews (with multiple questions each), the bug squash question gave us the biggest signal on candidates. Our question was far simpler: it was a simple class (java + python variants, no fancy syntax) and ask them to describe what it does, then find the bug, and finally ask them what they would change. It reflects a true test of what the day to day is, and whether or not the candidate would succeed in the role.