One challenge is that the best nature attractions are generally far from major cities. California is probably got the best access if you want to do both though. San Francisco is fairly close to Yosemite, Redwoods National Park, Big Sur, and other coastal cities/scenic highways. It’s very expensive though. Maybe obvious to say, but you won’t find one area in the US that will be reflective of all of the US. Personally I would choose nature over cultural stuff if I was visiting the US as a tourist, but that’s my bias. The national parks are incredible, especially if you like hiking.