Haleakala National Park is at the top of my favorites list. It is unique and beautiful and diverse. We spent almost a week exploring this park.
We didn't spend as much time at this National Park as I would have liked but there were a lot of very cool things we experienced at this park.
Zion is another one of my favorites. This park has so much to offer.
The Redwood National and State Parks are absolutely stunning and magical. They also make the top of my list of favorite National Parks.