I recommend the Motor Carrier's Road Atlas for planning, and the AAA state maps for more detailed navigation. You will also find some special series AAA maps (e.g., the Smokies, a great city map for Lexington KY that shows the scenic drives through horse country).
I recommend the AAA maps since they are consistent and good to use for navigation. Also, and this is very important, you can get new ones every year or so. You should have relatively recent maps so that road changes are reflected (just as you want a GPS that you can update maps).
P.S. My recommendations are based on a degree in Geography and 30 years working in the map making field.