Some say around about the time he sparked Ruddock out in 1992. This is a good shout, because he was 27 & at that age, you are in your physical prime.
Some say around about 1999 - 2003, when he was 34 - 38. He did have some impressive victories then, but he was too heavy & cautious for my liking.
I think he was in his prime between about 1995 & 1998, aged 30 - 33. He had some good victories during this period, seemed more willing to engage his opponents & had finally learned his craft, having improved from the Right hand happy slugger he was in his early days.