I recommend:
*
Lucrezia Borgia: Life, Love, and Death in Renaissance Italy*
by Sarah Bradford
I bought a copy of this two years ago and like it very much. Sarah Bradford, who has one foot in the scholarly camp and one foot in the popular, is a well-regarded biographer in the UK known for being fair and even handed. She paints a well-researched portrait of Lucretzia and dispels the canard of her as an incestuous whore and a poisoner.
There’s another book, The Borgias by Christopher Hibbert, that I haven’t read yet, though I’ve been meaning to get to it. Hibbert is a first-rate biographer. Like Bradford, he pens well-researched and entertaining works. I admire several other biographies he’s written, especially his life of Queen Victoria, and have every reason to expect his Borgias to be excellent.