The only times I bought Barron's was when I knew the material thoroughly and didn't need the first half of the book to teach me or refresh me on certain aspects (i.e., SAT Math II, SAT Lit, AP CS). When I actually wanted to refresh my memory on course material, I bought PR
(i.e., any AP test I was taking).
Barron's generally crams the most tests into a single book, which is good if you already know the material and just need the practice. Otherwise, the "teaching" in Barron's is generally horrendous and does not explain anything very well. A lot of times they focus on little things that come up rarely on the actual exam. Having said that, I have to say that the exams themselves are a little bit shoddier than those found in PR
, but they're good enough.
To me, nothing beats the first half of the PR
books. They tell you exactly what you need to know for the exam, and their end-of-chapter reviews are good. Their practice exams are known to be a little bit easier than Barron's (known to be the hardest, perhaps because they sometimes focus on obscure things), and they don't have enough practice.
Another big issue I have with Barron's is the egregious typos found in their books. For example, on a practice SAT Math II exam, the answer was "B" or something, and the listed answer was "D." In the answer explanations, it still said the answer was "D" but the explanation gave support for "B" being the answer. That's the most outstanding example I remember, but they occur often enough that I can safely make the judgment that PR
's quality is much better than Barron's, especially in this aspect.
So if you know the material and just want the practice, go for Barron's. Anything else, go for PR