I like the National Audubon Society field guide. I have not tried the National Geo. one yet. I have another one called "An Audubon Handbook." I don't like the pictures in that one as much, and it does not have range maps so it isn't as helpful for a beginner like myself.
I have 2 guides I use. The National Geographic Field Guide to the Birds of North America and Smithsonian Field Guide to the birds of North America. I prefer the Smithsonian because the photos are more individualized for the specific bird I am looking for. The National Geographic has photos grouped together on a page.