John Buford is one of those generals from the Civil War who deserves to be much better known than he is today. He almost became better known when he was played in the film Gettysburg by Sam Elliott, but I suspect nearly everyone leaving the theater came out without actually knowing Elliott's character's name. The two books about Buford that I am discussing here are:
General John Buford: A Military Biography, Edward Longacre, Combined Books, 1995
"The Devil's to Pay": John Buford at Gettysburg, Eric J. Wittenberg, Savas Beatie, 2014
I just finished Longacre, the older of the two, and decided a comparison and contrast would be more interesting than a straightforward review.
Longacre and Wittenberg are authors who have devoted much of their time to Cavalry operations, and both have spent a lot of time on Gettysburg in particular. Since Buford's finest hour as a Cavalry commander was certainly the first day of Gettysburg, both authors deserve to be taken seriously.
Longacre's book appeared in 1995, 2 years after the theatrical release of Gettysburg; Longacre served as an advisor for the film. In his Introduction, he explains that there is a dearth of some traditional primary documentation - Buford did not leave much in the way of written correspondence. Longacre had long regarded writing a Buford biography as unreasonable, but the film production persuaded him to try. The lack of correspondence can be seen in how the book is written, as in some places Longacre has to speculate mildly about things that a letter might have made clear (if there was a letter).
Wittenberg has a different task. He is focusing on Buford's military operations through Gettysburg, which are well documented.
Both authors hold Buford in high regard, and they are correct; Buford was almost certainly the finest Federal Cavalry commander of the Civil War (Custer's PR not withstanding). Longacre is a nice biography, but a bit light on maps. Wittenberg is more focused and detailed, and has a number of excellent maps. Wittenberg is in print, Longacre is something you'll need to find used.
Both are good books, it depends on what you're looking for.