Barron's vs. Peterson's for Physics

Which practice test is harder/more reliable? I get like mid to high 700s on Barron’s, but I do really bad on Peterson’s, sometimes not even scoring a 700. I’m aiming for a 770+ on the test on June 2. I’ve gotten an 800 once on a Barron’s practice test. Should I be worried about bad scores on Peterson’s tests or should I rely on Barron’s?