Big Bend is certainly a favorite, but you might want to start in southern Utah where you can hit five national parks: Zion, Bryce Canyon, Capitol Reef (another favorite, and so undervisited that it doesn't even have a gate as I recall), Canyonlands, and Arches- all breathtaking, with the bonus of Highway 12 between Bryce and Capitol Reef, the most dazzling road I've ever been on, and I've driven the Amalfi coast highway and Chapman's Peak in Cape Town. Another bonus is the cliff along the Colorado River in Moab (right near the Arches entrance), with lots of nifty petroglyphs. Acadia is very small but special (there's only the Blue Hill Peninsula between our summer place and Mt. Desert Island). I'd especially like to see Isle Royale in Lake Superior.