I don't know the criteria, but I think it should be a fighter who had a significant presence in the elites. That doesn't necessarily mean a champion but maybe a guy who had several great fights who was at least 50/50 with people in the top ten.

And just because a guy won a belt doesn't mean he should be in. Like Jose Antonio Rivera. A decent fighter but he was completely out of his depth in his first defense of the WBA title.