My personal timeline for who's #1 PFP is like this:

From around 1990-1993, it was Chavez and Whitaker as 1a and 1b.
Then when Whitaker beat Chavez, he became undisputed #1 and stayed that way until about '95.
Then as Whitaker started to show up out-of-shape, he and Jones became 1a and 1b, and it stayed that way until '97 when Whitaker lost to DLH (even though I thought he won.)
Then Jones was undisputed #1 from '97 until he lost to Tarver, at which point Hopkins took over. He was #1 until he lost to Taylor, at which point Mayweather moved up to #1. And Mayweather has been #1 ever since.