I have seen Bison take a lot of killing, one took 5 good hits with a 300 WBY and went at least 5 miles to die..My grandson shot one bull twice in the lungs with a 50 Beowolf and it made two miles. I have seen one cape buffalo take 13 good hits with a 500 N.E. and another tatke 9 with a .470 and a 500 and I have both of those hunts on film..
What makes animals hard to kill is mass, size in other words..What makes a Cape Buffalo meaner is being chased by Lions all night and hunted by man all day, they stress...Bison can be every bit as agressive but very seldom do they charge, but when they do they are a sight to behold..I think the same applies to the Water Buff of Australia, they are fairl docile but when the anger they are damn hard to stop, as they are the largest of the three.
All animals will fight under the right circumstances, Sable, Gemsbok, and bushbuck can be dangerous..A Rhino is always dangerous and so is a Hippo or Elephant..I have no clue which one is the worst, but the Lion puts me on edge more than any other animal. I have been a part of one lion charge and it was very impressive to say the least.
Circumstance determine which one is the baddest kid on the block.