I genuinely don't have a clue at the moment, several candidates (add Knocky and Stocko to those you mention at least). Long way to go. Agree though that Duffy has been brilliant so far.
Based on what he did to Martin today, it's literally anything that comes to him at any height. One challenge was just in front of us and it was like listening to a rugby tackle - a noticeable thud as they came together. Duffy jogged away, grinning slightly. Martin was on the floor, obviously.