Our Woodall's is stashed in a bin most of the time. The print is tiny, it's major city phone book size, and lists more rv parks and resorts than anything else.
I pick up state maps and campground literature at the welcome site, and keep a collection. If I have time to plan ahead, I find the state park websites for each state to be quite helpful. "Camping with the Corps of Engineers" is a great little book for states that have a number of COE parks, though it's not complete, either.
It's also helpful to check National Forest Parks for the states you're visiting/traveling. We like those, too. Personally, I'm not so keen on the big National Park Campgrounds. We're more likely to look for a state park nearby. Absolute last choice is an rv park/resort for us... Not our style.
PS Ordering the state maps ahead of time is a great idea. Many of the state maps list most, or all, of the state parks with camping facilities on them, and are very detailed and helpful as a planning tool.