I don't think Chuck or Wand belong on the list. They've been in the game far too long and have taken probably three times as many hits in the head. We've all seen them take serious damage, but after absorbing a super KO punch it's really hard to be 100% ever again mentally and physically.
Alessio is definitely there.
I'm surprised Stefan didn't get KOed. He looks like a clumsy giraffe although he's fun to watch.
CHINS OF STEEL
I would include The Talent, but I seriously hate that guy. He's fricken goofy. Can't wait til he gets KTFO.
Honourable Mentions: Oleg Taktarov or Don Frye