Maybe there were better horse racing writers back in the glory days, but in my lifetime it was Bill Nack, who died from cancer today at 77. He chronicled Secretariat's Triple Crown year of 1973, and wrote a poignant farewell two decades later.
http://www.espn.com/horse-racing/triplecrown2014/story/_/id/11032695/my-years-chasing-triple-crown
http://www.espn.com/horse-racing/triplecrown2014/story/_/id/11032695/my-years-chasing-triple-crown