Guides - Frommer's vs. Woodall's

Which one would you recommend. I have heard that Woodall's frequently gives good ratings to campgrounds that don't truly deserve it. I have not heard much, good or bad, about Frommer's. Not sure if that is a good or bad thing. I would like to limit my purchase to one all-purpose book (not different regional ones) since we will be traveling cross-country and I don't want to carry a bunch of books with us. TIA for any advice!