Mark Hunt's chin is great. However, not only has he been stopped much less often, I give Roy the edge because of how much better defense Hunt has. Hunt doesn't eat things as flush as Roy does. Roy walks into straights and uppercuts and gets caught by bombs with no head movement. Mark is actually a legit technical striker, so in the average fight he doesn't take the same kind of frequency. I don't think Hunt would have survived the beating that Stipe put on Nelson at 181, with something like 100 significant strikes to the head. Yes, Hunt made it to 5 rounds in his own fight with Stipe, but Hunt is a more legit defensive fighter and didn't get beat up in the same way.
Big Nog has a very good chin, but what made him so tough is recovery. He could get rocked and dropped, but he didn't quit. Bob actually knocked him out with the piledriver, but he was jolted back awake by the punches and went back into it. I'd put him in a general toughness list, but I'm not sure about pure chin. The GnP from Fedor wasn't really composed of knockout punches, so Nog's ability to survive was largely toughness, not some kind of freak chin. I'd actually put guys like Rothwell above him in a list of this format.
Fujita for sure belongs up there. What must be noted however, is that he fought smaller guys than Roy and his chin had a shorter life. Wand is a LHW and he stopped Fujita with punches. Roy has been tough his entire career up to this day.