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.
Not to knock Pius X and his wonderful writings, but what really cuts the mustard is the actual bishops he appointed.