Both these guys have shown absolutely ridiculous ability to soak up punishment over the course of their careers, but who in your mind had the superior chin? Wach took huge shots off Wlad, Bakole, Povetkin, Miller, Whyte and has only really been seriously hurt by Makhmudov when way past his prime. Rudenko has taken shots off Zhang, Povetkin, Kabayel, Browne and was only hurt (to the body) by Kabayel and Anderson. I can't recall him ever getting hurt upstairs. If I had to bet I'd pick Rudenko by a hair, but both men are head and shoulders over almost every other HW of the past decade at least. The head swiveling shots Rudenko took off Zhang would have dropped a... juggernaut EDIT: haven't seen the Sirenko fight so might be in error with my above post.
What Wach took from Wlad (one of hardest hitter in history) is just crazy. He always was slow so he cant react and eat full power right hand many times. He for sure was heart but not go down. I think after later rounds Wlad seems to give up with trying to end him to not get to tired... For me Wach. With all his limitation he for sure got chin on level 10.