And JPII’s and BXVI’s choices.
I asked someone who knows infinitely more Church history than I do who he thought was the last Pope who seriously made holiness and orthodoxy the top criteria for bishops. He said he’d have to get back to me. Hasn’t yet, and its been several months.
Given this Apostolic Exhortation written by Pope St Pius X to Catholic Clergy, I would argue for Pius X:
http://www.papalencyclicals.net/Pius10/p10haer.htm
It just so happens he is also the author of Pascendi Dominici Gregis which warns us of the Modernists in our midst.