Different criteria brings about different lists. Retherford, Taylor, Ruth and Bo have all been listed as #1 by someone in this thread. I'll add Jason Nolf, and make them 1a, 1b, 1c, 1d, and 1e, they are that close.
Retherford is the only one that did not benefit from a redshirt year in his true freshman campaign. He's the only one of the five that did that.
Taylor "only" has two National Championships, the other four wrestlers have three each.
Taylor, Nickal, and Nolf are the only ones that were four-time finalists. Zain has a 5th place finish, and Ruth has a 3rd place finish.
All five wrestlers have three career losses, which I find very interesting. The number of wins are different as wrestlers had more matches during the Taylor/Ruth years.
Nolf is the only one to win a championship on one leg for the tourney, though Ruth gets credit for coming back to place 3rd after an injury during the tourney.
As far as career NCAA Points, all-time and all teams; Taylor is 5th (99 pts), Nolf is 7th (98 pts), Nickal is 8th (95.5 pts), Ruth is 10th (94.5 pts), and Retherford is 11th (93.5 pts). So Penn State has 5 of the top 11 right now. Joseph and Hall would have surely been top-20 on this list.
I do believe that McCoy, Megaludis, Prescott, Martin, Hall, Joseph, Matter and others belong near the top of any all-time Penn State list.
Someone else mentioned the difference in competition. Two of Retherford's losses were to Stieber, two of Taylor's losses were to Dake. I believe this should be a consideration, but it gets messy when one starts using this level of detail to differentiate careers.