My one interview question (I have a series of related but only go down them selectively) is “tell me the one thing you’ve done that made you the proudest of what you have achieved or the happiest with what you were doing, don’t worry whether it was the most impactful or important from an outsider’s perspective”. I am trying to give people the chance to show me the best they have, not a competition for me to prove myself I am better somehow. You will be surprised how many interesting discussions and learning opportunities I got out of this question. Everyone who has peered interviewed with me ends up using it in their future interviews.
I ask a variation on this: "tell me about the program you're proudest of."
And also:
"What's your favorite algorithm or data structure? It doesn't have to be the fastest or best, just your favorite? Why?" (This does have one right answer: shellsort.)
"Tell me about a time you made a mistake — not a time where one of your weaknesses turned out to be a strength and you saved the day. No. Tell me about a time you really screwed up."
It does not work very well for new grads. In grads case I question the purpose of interviewing at large. They studied, completed one goal, all we have to do is give them the tools to understand their next steps. With grads I focus more on their interests, what they are reading on the subject matter domain (data in my case), etc. There’s no really silver bullet and the value of this question even with experienced hires is the follow up where you drill down on technical and behavioural elements of what made this project/product the one they chose to discuss.
No numerical scale, you either want someone in your team, or not.
