Rigorous Schools and Classrooms is for someone who needs background to understand what rigor is and needs a basic grounding in such topics as school culture and school change. Although this book is practical – it has 33 tools -- its emphasis is on concepts.
On the other hand, Rigor in Your Schools: A Toolkit for Leaders was written as a response to reader requests for more implementation tools. There are 97 tools in this book to help school leaders implement rigor in their schools. Although the red book contains a brief review of the concepts, its emphasis is on the tools.
Newer principals, Board Members, and anyone without much background, should go with the blue book, Rigorous Schools and Classrooms. If you are experienced and want lots of implementation tools, go with the red one, the Toolkit.