IMHO, those are the two best NA field guides. The Peterson and Kaufman guides are widely regarded as the most beginner-friendly. However, I used the Sibley guide as a beginning birder and it served me very well. It's unmatched in terms of the variation depicted and has other features that I really appreciated (i.e. tells what months the birds are in their different plumages).
Other tips? Where do I start....
For field guides, I have two other recommendations. I'm a proponent of having different kind of guides. Your two use paintings, so it would be a good idea to get one or more that use photos.
The Crossley ID Guide (
my review) is great for studying and learning birds before going into the field. Another good photographic reference is
The Stokes Field Guide to the Birds of North America (
review).
From there, I've got some more suggestions if you're interested. I'm trying not to throw too much out there at once.