I'm a Fury fan, but I think he's got the weakest chin of the bunch. He makes up for it with superb defence and recovery skills, and the heart of a lion. Unless he's knocked unconscious I can't see him ever getting stopped. Wilder I think has actually got a pretty solid chin. He gets rocked and buzzed on occasion, but since he's hit the big time he's been in with some solid punchers and not his the deck. That's despite having a ten cent brain and a ten cent defence. Joshua's also not got a bad chin. His trouble is his huge muscle mass leaves him immobile and prone to gassing, which means when he tends to get hit with punches a lot flusher than the other two.
Power is usually the last thing to go, and I don't believe Pov rocked Joshua... Joshua lost balance by his own admission. All heavies can lose balance when they are being pounding on the glove guard by an heavyweight opponent.