I bought two books on portrait photographers recently and because of the similarity I decided to review them together. Although the Karsh book is sub-titled "A Biography in Images" that could describe both books although the Heisler book would more aptly be called a retrospective. The format is similar in both, a series of photos with text about the image, the person photographed and the making of the photograph although not technical information (Camera used, f/stops,film, etc.). There is some casual mention about lighting or other aspects of the shoot for the photos but if you are looking for a "how I shot this" book you will be disappointed. I wasn't looking for that and wasn't disappointed in either book.
I bought the print versions. The Gregory Heisler book is also available for Kindle but in my humble opinion the photos need a large print book for their full impact. Both are printed well on high quality paper and nicely bound coffee table sized volumes.
I read one criticism on a forum that the Greg Heisler portraits were too editorial and not a personal expression or "art", an unfair criticism I think given that Gerg Heisler's portraits were in fact editorial assignments. He brings to them a degree of art but working within the constraints of a client always brings some level of expectation from the client as well as the constraints of the sitter. The story of the cover image (Muhammed Ali's masseur) in particular demonstrates Greg's ability to deal with such constraints and still get a powerful and revealing portrait.
Yousuf Karsh was a commercial photographer as well and many of the portraits in his book were also made for magazines although I personally see more of Karsh in his portraits than I see of Heisler in the Heisler book. It's a matter of degree and is subtle, varying from image to image but overall Karsh seemed to transcend the 'assignment' to a greater degree than Heisler. The Karsh book also includes a brief biography and some non-portrait photos at the beginning which helped give context to the portraits that followed. I came away from the Karsh book feeling like I had met the photographer rather than simply going to an exhibit of his work.
If you are interested in portraits of (mostly) famous people and learning a bit about what it was like to encounter each of their personalities as a photographer I highly recommend both books. I don't have links to Amazon and don't get any 'affiliate' fees from them if you buy either book. In fact, although I got them through Amazon, if you are fortunate enough to have a local bookseller who stocks them I encourage you to buy them there. As much as I like Amazon they have killed off many local bookstores to the point that there aren't any near me who carry this sort of book.