My opinions on the best books in categories....
General History of the Park: The Wild East by Margaret Lynn Brown
Comprehensive History of the Area: Strangers in High Places by Michael Frome
Cades Cove Specific History: Cades Cove by Durwood Dunn
Fishing Specific: Jim Casada's Fly Fishing in the GSMNP
Hiking & Camping: Hiking Trails of the Great Smoky Mountains by Ken Wise