John,(posted 8538 days ago)Get both.
The Darkroom Cookbook is more of a general and comprehensive B&W guide. It covers most things related to B&W darkroom work: film development, printing paper development, chemicals, and all darkroom related processes.
The Film Development Cookbook is much more specific to B&W films and their developers. It extensively discusses the choosing and handling of B&W films of all types and brands, and gives in depth information about selecting and using all known B&W film developers. The development charts alone are worth the price of admission.
Good luck, Sergio.