Written by a popular American biographer, this book is quite thorough. But it's also quite readable, and with only 636 pages of text (in a pretty reasonably-sized font!), it gives you the big picture of FDR's life without overwhelming if you with details. If you want to read one big book about FDR, this is the one to choose.
Brands is a master storyteller and is well known for his biographies of major American figures, Andrew Jackson and Ben Franklin among them. This book is quite readable, but it's also long, clocking in at over 800 pages of prose. If you want to curl up by the fire and read an FDR biography, this is the one to go with, but don't expect to finish it overnight!
The author of this book is a rather FDR-like figure himself: a newspaper magnate, he was once one of the most powerful men in Canada. He's also an excellent writer, and though this book is quite long (1134 pages of text!), it's readable, with a decidedly pro-FDR spin on things.
Written less than twenty years after FDR's death, many historians consider this book to be the definitive account of the New Deal. Leuchtenburg both analyzes the economic impact of the New Deal and tells the story of the political machinations that drove its creation.