[joeax]

I've been on both sides of the table and I'll tell you a coding challenge is a much better solution than the whiteboard/leetcode/code-on-the-fly during the interview. Just keep it short i.e. 2-4 hours max.

As far as alternatives to a coding challenge, the OP did suggest walking through a prior project on GitHub. I think that's a great idea (in addition to a coding challenge though); an open source project on GitHub is a bonus for a candidate, and will in many cases steer the interviewer to ask questions about your project in lieu of abstract concepts.