There are lots of bird guides out there now, and to be honest, I haven't looked at most of them. From what I've seen, Sibley's is still the best. I bought the full North America guide shortly after it came out. It has more thorough coverage of the eastern birds than the Eastern Birds guide that came out a few years later. If you want a field guide, the smaller version is the way to go. If you want a reference for when you get home, go for the full version.
I still really like Peterson as well. It`s great for highlighting the differences between similar looking species. I find his illustrations more accurate and representative of typical plumages and postures than many others that look more detailed. His `confusing fall warblers` plates are a great feature that I don`t think I`ve seen anywhere else.
BB