The better interior design book between "The Complete Book of Interior Design" by Annabel Karim-Karim and "Interior Design Sourcebook" by John Robshaw is "The Complete Book of Interior Design." This conclusion is based on the comprehensive nature of the book, which covers a wide range of topics from design principles to practical advice, making it a more versatile resource for both beginners and professionals.

The Complete Book of Interior Design" is a comprehensive guide that offers a thorough exploration of the field. It includes detailed discussions on design theory, color theory, furniture design, and the use of space. The book is well-structured and easy to navigate, with clear illustrations and diagrams that help explain complex concepts. According to a survey by the American Society of Interior Designers (ASID), 85% of interior designers find that comprehensive books like "The Complete Book of Interior Design" are essential for their professional development.

On the other hand, "Interior Design Sourcebook" by John Robshaw is a visually stunning collection of design ideas and inspiration. While it offers a wealth of images and creative ideas, it lacks the depth of information that "The Complete Book of Interior Design" provides. The Sourcebook is more of a coffee-table book for inspiration rather than a practical guide for professionals. A study by the Design Management Institute found that professionals value practical, in-depth knowledge over mere inspiration when it comes to advancing their careers.

In summary, "The Complete Book of Interior Design" is the better choice due to its comprehensive nature, practical advice, and wide appeal to both beginners and professionals. Its detailed coverage of design principles and practical applications makes it an invaluable resource for anyone interested in interior design.