Justin Taylor has been interviewing professors and pastors to get their list of top biographies (about Christians and non-Christians) including Doug Sweeney, Carl Truman, George Marsden, Mark Noll, Kevin DeYoung and several others.  The leading recommendations across all of the contributors were:

• George Marsden’s Jonathan Edwards: A Life (9 votes)
• Peter Brown’s Augustine of Hippo (6 votes)
• Roland Baiton’s Here I Stand: A Biography of Martin Luther (5 votes)
• DG Hart’s Defending the Faith: J Gresham Machen and the Crisis of Conservative Protestantism in Modern America (3 votes)
• There were several with two votes, which you can see here

There were also several recommendations of John Wesley, but no two by the same author.  The list is noticeably short on books about women.  See this link for a list of biographies of Christian women