Barron's Music Theory vs Complete Idiot's Guide

<p>For someone self-studying AP Music Theory, what book would be better, Barron's or Complete Idiot's guide? Especially for learning the most theory and improving someone's skills at composing music on the piano? I care more about learning the most as opposed to test taking strategies, so thats why I wanted to know how Barron's compared to other books and which book I should get (I can only afford 1 book, so don't say both).
THANKS!</p>