It's impossible to choose THE best Madeira walking guide. Ideally, buy two or three, otherwise this may be the one.
It offers an extensive range of walks, with much practical information presented attractively. There are excellent supporting pictures that do not dominate the text. Very importantly, the book is well bound and eminently pocketable. Everything I look for in a walking guide.
If you can afford one or two more, go for the Cicerone book by Paddy Dillon, and consider the Sunflower Landscapes book by John and Pat Underwood. I prefer the former, but the latter does have good pictures, a useful map, and car tours as well as walks; unfortunately it is an awkward shape and the binding is not as good - the book does not like to stay open, and looks as though it may fall apart prematurely.