I think that the closer you can simulate relaxed day to day coding, the more representative the results will be.
White board questions can be pretty stressful and probably not an accurate reflection of a candidates true capabilities. I.e. someone with a lot of practice interviewing may do great and a great coder may choke. Think about it; how many times have you slapped your forehead as you drove away from an interview because of something you absolutely knew the day before but suddenly couldn't remember during the interview?
My fantasy interview would be to pair program on a small project that neither of us had seen before. This would seem to be a lot less stressful than the normal barrage of test questions.
draw a circle with C#
http://sockpuppet.org/blog/2015/03/06/the-hiring-post/
And the HN discussion
https://news.ycombinator.com/item?id=9159557