For SAT subject test physics, both books are best. Barron's has practice exercises and tests designed the same way as college board. In fact the questions in Barron's are more difficult which prepares you for the test really well. On the other hand Princeton Review gives you theory based preparation. It has long chapters explaining the concepts. You should learn the concepts by Princeton Review and then solve the exercises in Barron's as Barron's does not give any detailed chapters on specific topics. So if you think you have forgotten what you learned back in high school, you should consult both books.
Third book is for the strategies and tricks that will save your time in exam. This is also by the Princeton Review and you should give it a look after you have completed the first two books.
Below are given the links to websites where you can buy or download the book as PDF.


1.Cracking the SAT Physics Subject Test, 2013-2014 Edition (College Test Preparation)


                          

The 2013-2014 edition of Cracking the SAT Physics Subject Test includes:

· 2 full-length practice tests with detailed explanations
· Accessible, engaging subject review, including coverage of Newton's Laws, work, energy and power, linear momentum, rotational motion, electric potential and capacitance, electromagnetic function, motion, oscillations, thermal physics, optics, waves, circuits, and more
· Tons of sample problems and drills


2.SAT Subject Test Physics (Barron's SAT Subject Test)


                        SAT Subject Test Physics (Barron's SAT Subject Test) by [Robert Jansen, Greg Young]

This edition includes:
  • Three full-length practice tests that reflect the format, timing, and difficulty of the actual exam
  • One diagnostic test to help pinpoint strengths and weaknesses
  • Answers and explanations for all questions
  • Extensive subject review of all topics on the test, including mechanics, electricity and magnetism, waves and optics, and thermodynamics
  • Appendix with equations, physical constants, and basic math review
  • Tips on solving problems quickly and advice on mastering difficult concepts


3.Cracking the SAT Subject Test in Physics, 16th Edition: Everything You Need to Help Score a Perfect 800 (College Test Preparation)


                         

Physics can be a tough subject to get a good handle on—and scoring well on the SAT Subject Test isn't easy to do. Written by the experts at The Princeton Review, Cracking the SAT Subject Test in Physics arms you to take on the exam and achieve your highest possible score.

Techniques That Actually Work.
• Tried-and-true strategies to help you avoid traps and beat the test
• Tips for pacing yourself and guessing logically
• Essential tactics to help you work smarter, not harder

Everything You Need to Know for a High Score.
• Expert subject reviews for every test topic
• Up-to-date information on the SAT Subject Test in Physics
• Score conversion tables to help you assess your performance and track your progress

Practice Your Way to Perfection.
• 2 full-length practice tests with detailed answer explanations
• Sample review questions at the end of each content chapter, plus final drill sections to test your comprehension
• Robust, easily reviewable summaries that emphasize core concepts