Kane vs. Abyss
In my opinion, here is the breakdown:
Kane has everything going for him ringwise. He has power moves, strength, he has a good top-rope offense, and very painful sounding uppercuts. He also is known for never tapping out and rarely running from a fight, even as a heel.
Abyss has strength and probably somewhat of a size advantage. He also has hard hits and numerous power moves, along with a high threshold of pain. HOWEVER, Abyss lacks a good aerial offense and seems less coordinated than Kane. For example, knocking Kane over the top rope usually leads to him landing on his feet whereas Abyss just lands on his ass. Abyss has also been known to run from fights and hide away in fear of his opposition.
Therefore:
I would say in a one-on-one fight [totally ignoring the scripted nature of pro-wrestling of course] Kane would win. The two would probably be equal on the ground-and-pound part, slugging it out for several minutes. But then Kane would use his athletic superiority on the top rope and in general (he does have a drop kick after all, something I've never seen Abyss use) to get the edge. Finally, with him beaten down, Kane would then find an opportunity and chokeslam Abyss straight to hell.
