I'm sorry to say that, despite its many ungrounded assumptions and uncritical reliance on received opinion, the best biography is still that of R. C. Bald, whose failings are mainly the result of his not having been able to read a critical edition of Donne's letters. We all hope to have one soon.
Thank you so much for your reply. I'm reading the R. C. Bald biography now. When you mention the uncritical reliance on received opinion, are you referring to his trust for Walton? What others? Can you, or anyone else on the forum, briefly mention the areas that are suspect?
The best way to answer your question about Bald is to read everything Dennis Flynn has written! Start with his critical biography of Donne's early years: _John Donne and the Ancient Catholic Nobility_. I'd also recommend the special issue of the _John Donne Journal_ that he edited (Vol. 14) along with many articles that he has published over the years in that journal that deal specifically with the use of archival evidence to reconstruct Donne's biography.