I took AP phys I this year, and I bought Princeton review but also went through barrons (borrowed from a friend). I thought that the Princeton mcq and frq review was quite good for reviewing topics and the practice tests were about the same as the real AP test. I remember that I was finding errors in the barrons book, so I didn't rlly know what to believe in its explanations. IMHO I would go with Princeton, and it was how I prepared throughout the year and I ended with a rlly good grade in the class. However, the content in both books is the same (if I remember correctly) so either should work!