Grant Amaral's book is the most complete one, with a lot of runs. Although it was printed in 1990 it is fairly in depth to a degree. Some might argue that a guide book written in the 90's is out of date, and the difficulty rating's of the run's are off. I've found that it still holds true on the big water runs, the author's backyard run is the North Fork Payette, which is Idaho's standard of class V. Were as the CCRC book's standard for class V is something like Gore, give or take.
The new book- The Idaho Paddler Whitewater gem's by Sean Glaccum was printed in 2009. The book highlights most of the standard classic's with a down rated scale of difficulty compared to the other book on some run's, they give one rating for the whole section, and don't factor in flow's, which is fairly important in Idaho with all the big water run's. The book also has beta on a few new creek's, and park and hucks that have been discovered with our modern day short boat's. It's a great book with full color pics, kinda like White Water of the Southern Rockies, but much slimer, but they did miss a few classic's like Meadow creek and Lolo creek. In general the descripts are not in depth, to give you the discover it for your self kind of feel.
It's nice to have both, but Amaral's isn't easily available. So if you use the new one cross check the ratings on American Whitewater as they relate to flows.