It depends on what you like to see and how much time you have.
Hmmm. You could head to Flagstaff and 89 to 160 to 163 and see Monument Valley, the Mexican Hat Rock, Valley of the Gods, and the Twin Rocks at Bluff. Then head east on 162/41 to 160 to 491 into Cortez CO, then follow 145 into the scenic mountains and to Telluride. Then 62 to Ridgway (consider unhooking and taking the truck south to Silverton & back), 550 to Montrose, and 50 east where you can visit Black Canyon. Continue to Salida, then 285 north to 24 east to Pike's Peak, Garden of the Gods, and Colorado Springs.
From there the plains scenery gets a little bland IMO until you get into MN. But coming back you could hit Mount Rushmore, Custer SP, and Devil's Tower on your way to the Tetons. Yellowstone will be crowded, but the Grand Tetons are not nearly as busy (campsites can be found without reservations) and the mountain views are very worthwhile. Heading south from there past SLC, you could follow 89 south where it somewhat parallels the expressway. Or take US-6 west to visit Great Basin NP, then 93 south to see Cathedral Gorge SP.
Maybe these locations sound good to you, or maybe not. You can always get a road atlas and pinpoint places you'd like to see, then look for the scenic highways (indicated by dotted lines) that will connect these places.
Mike G.
Liberty is meaningless where the right to utter one's thoughts and opinions has ceased to exist. That, of all rights, is the dread of tyrants. --Frederick Douglass
photo: Yosemite Valley view from Taft Point