So many routes North
You have plenty of choices on how to cross the USA, south to north. CA is seductive, so many parks and the PCH. But crowded and expensive. AZ, UT and north offers some of the best scenery in the world, empty and easy going. NM, CO, WY are perfect, dry, high altitude. I've done all your choices several times and I can't say which is the best. Get a National Parks annual pass, you'll need it.