Best” is somewhat meaningless. Each trip should be a new adventure or a relaxing respite, whichever you need.
Glad to see so many fellow Zion lovers, including the Subway; try no-trail random cross-country and canyon bottom hikes on the eastern and northern sides of the park for more solitude, too. Canyonlands 4WD for no humans, yep. I’d recommend Utah’s Big 5 in winter, especially Bryce. No crowds, snow like frosting on everything, elegant ice formations where falls and creeks freeze. There’s a lot beyond the big parks in UT, too, like the slot canyons near Escalante (Peek-A-Boo, Spooky and Zebra, for instance), Goblin Valley & Little Wild Horse Canyon, Yellow Rock, Hole-In-The-Rock Road, the whole region around Vernal - - Dinosaur NM, Fantasy Canyon, Flaming Gorge, etc.
Montana is another underrated state. Most folks know about Glacier and should see it before it melts (and don’t forget to try some Huckleberry treats while in the area!), but add on the Bear Tooth Highway, the mountains just outside of Yellowstone around Gardner and West Yellowstone, the Lewis & Clark trail, the dinosaur fossils and badlands of Makoshika, Terry Badlands, tons of old mining and ghost towns like Garnet, Virginia City and Nevada City, the National Bison Range, prospecting for sapphires in some small towns, Missouri River wildlands, Great Falls, … I could go on.
Long road trip? Drive Route 66 end to end and make the stops on it; that’s was a kick, even better when you look into what’s happening along the way and time it to see some events, concerts, fairs, etc. (post-covid). Pacific coast? Go all the way from Port Angeles, WA to San Diego on the 101 and Highway 1. Olympic NP, lots of nice towns and beaches along the Oregon coast, Redwoods and quiet northern CA towns before you get to the bay area (take the “Lost Coast” spur just south of Eureka, CA rather than the 101 there).
Fall foliage? Try West Virginia, Utah, upstate NY and PA, MN (I agree, MN’s “arrowhead” is under-appreciated), or the Ozarks as alternatives to New England. All are great.
Overseas? Don’t rent a car, rent a camper, even in Europe! We’ve done that in Australia, New Zealand and Italy-to-England-via-France. All were great trips, and you meet more locals that way, e.g. in campgrounds, at groceries, etc. You can walk from camps to the Leaning Tower of Pisa, Chartres Cathedral, beach on the French Riviera and Cinque Terre towns in Italy, among others.
Do the eastern side of the Sierras along US 395 rather than the western side crowds in Yosemite and Sequoia. Try the ten-lake loop trail around Saddlebag Lake just east of Yosemite’s Tioga Pass entrance. Or go to Lassen NP in northern CA and get “Yellowstone Junior” with no traffic.
“History buff? Try Virginia, Presidential Libraries, Lewis & Clark route, Revolutionary or Civil War sites. There are more railroad (try Sacramento), historic aircraft (try Rheinbeck, NY) and antique auto museums (try Reno) than you’d imagine scattered around the country. (We’ve lost track, pun intended.) Find some old Country Stores that still survive. You want odd? “Carhenge”, the “Cadillac Ranch” and the Winchester House fit the bill. Grab a “Weird State X” book and take a drive. But GO!