Thank you, Kyle! That's a great question. It depends a little bit on your specific interests and also which part of the country you're visiting. Yellowstone is one of the most spectacular and unique parks, but the downside is it's incredibly crowded, and also quite far away from major cities. On the other hand, Saguaro and Indiana Dunes are great from the standpoint that they are easily accessible from big cities with airports (Tucson and Chicago, respectively).