“The Rails 4 Way”, by Obie Fernandez and Kevin Faustino is a great reference book that covers most of what a Rails developer is likely to need on a daily basis. It covers the various DSLs and idioms (i.e. route definition, controller filter declaration, ActiveModel association and validations, etc) without getting into the details of Rails internals and how those features are implemented. The explanations are clear and the code examples relevant.
Just like Rails itself, “The Rails 4 Way” is opinionated and occasionally differs from the omakase 1 way; Most notoriously, but hardly controversial, using Haml as a template engine and Rspec for testing.
Most of the book can be read cover-to-cover or used as a reference on particular topics. The exception is section about rails helpers (Chapter 11) which, as the author themselves point out, is really just an alphabetical listing of the methods available, like the one usually found on appendices or online documentation.
I recommend this book to new Rails developers (maybe after trying out an online tutorial) and for experienced Rails developers who are still working on Rails 3 (or 2!) and are expecting to make the jump to Rails 4 in the near future.