I would say the guy I saw who got the best leverage to the body ever was Mike Tyson in his prime, but guys figured out how to stop him from ever getting the oppertunity relatively easily.

I think Cotto has the most powerful body shots today, and he seems to have the best accuracy with them as well. He has the intuition that allows him to land at will to the liver.

A guy not mentioned is Chad Dawson who IMO throws very well to the body, he just doesn't seem to have the power to hurt guys down there.