I've been comparing Westerfield's book to Canepa's book, and it is fascinating to me how different (in a good way) both books are addressing the same topics...it is great to have two different approaches to a topic that complement each other and offer something different, rather than carbon copy each other. Bottom line: get both, you won't be disappointed, and you will be better off than having only one or the other.
Obviously, Westerfield's book has better treatment of more modern innovations, such as GPS (where Canepa's book, from 2005, mentions it briefly in 2 spots).
I was going to make a joke about the books being what you would expect if a lawyer wrote one book (Canepa) and a physics major (Westerfield) wrote the other, but that would be a gross oversimplification and would also be wrong. A good example (of my bad, gross oversimplification) might be how each handles calculating how much black powder to use for an ejection charge. Canepa has a page where he refers to another book and websites for the equations, and then gives a rule of thumb equation from an altimeter manufacturer. Westerfield has three pages of discussion and formulae starting with the "ideal gas law" and derives the equation to determine separation force, but then tells you at the end of the section to refer to a table on the next page "because it is a bit tedious to do...for every rocket." It is two different approaches...
I really like the way Canepa includes hundreds of photos with his discussion and instruction. I was surprised at that fact there weren't more photo's in Westerfield's book, but the ones he has are in color and at a better resolution.
I'm still going through them...bottom line, get both books! And I'm not being wishy-washy, at least *this* time.