Which field giude is better for the Science Olympiad event known as Ornithology?

Is it:
National Audubon Society Field Guide to North American Birds, Western Region
or
National Audubon Society Field Guide to North American Brids, Eastern Region?
edit: The region I live in has nothing to do with it, Science Olympiad has a very specific list of birds to work with. I just wanted to know if anyone had done the research and found out the better book.

I prefer the Peterson field guides to either Stokes or Audubon (it was what was recommended when I was studying Ornithology at Humboldt State). For either Peterson or Audubon, get the one that’s applicable (i.e. if you live in the west, get the Western book). If you’re not sure (because you live in the middle of the country, or ?), look at the introduction of the book, and it will tell the areas it covers.

edit:
Having looked over the list, I think you may need books for both the East and West. There are birds specific to both regions on the list (e.g. Eastern bluebird and California condor).

How to Identify Birds by Sight : How to Record your Bird Sightings

Random House 103850 National Audubon Society Field Guides to Eastern Northen American by Birds John Bull $19.95 Introduced in 1977 and completely revised in 1994, these bestselling photographic field guides have become the birding bibles of more than four million enthusiasts. Virtually every bird found in North America is brought to life in a full-color photograph and with textual information on the bird’s voice, nesting habits, habitat, range, and interesting behaviors. Accompanying range maps; overhead fl…

National Audubon Society Field Guide to North American Trees: Eastern Region $8.20 For the untrained observer, it can be quite a challenge to sort out the many trees that make up a stand of older forest in, say, New England or the Ozarks. This well-illustrated guidebook, covering 364 species, comes to the rescue with photographs organized in several ways: by, for example, the shape of the leaf or needle, by the fruit, by the flower or cone, and by autumn coloration. Followi…

National Audubon Society Field Guide to North American Birds: Eastern Region, Revised Edition $9.29 Covering 508 bird species found east of the Rocky Mountains, the revised second edition takes into account changes in taxonomy and uses improved photography. At the heart of the guide is a set of 646 well-made color photographs whose subjects are organized by easily discerned characteristics (e.g., “chicken-like marsh birds,” such as the clapper rail; “gull-like birds,” such as the kittiwake;…

The Sibley Guide to Birds $17.99 North America’s definitive guide to birding. This is the newstandard for serious birding enthusiasts. Over 6500illustrations of 810 species….