I like Dr. Oz the best, so far, hands down. I know absolutely nothing about him outside of this, other than that he's a talk show host. I think he's been the most comfortable and the smoothest guest host to this point.
Aaron Rodgers is horrible. Hard to watch/listen to.
I thought Mike Richards was good, but not great. Ken Jennings ... no. I found Katie Couric very dry, stoic, robotic and boring.