What got me thinking about this question was re-visiting, for umpteenth time, Andre Kertesz's book, "On Reading".
Much as I love landscape and travel photography, I'm starting to appreciate social documentary / reportage photography. There are, of course, hundreds if not thousands of great photographers in this genre, but "On Reading" is such a great piece of work by someone whose other urban landscape and pictorial / abstract work I really like, that I'd love to have been able to "shadow" him and watch him work for a while, if not spend time discussing his motivations and techniques.