I've done western US National Parks tours in 2013 and 2016. If you want to start in Vegas, I recommend going to Zion, Bryce Canyon, Arches, Monument Valley, Grand Canyon, Hoover Dam and back to Vegas. About 20 hours of driving time, but well worth it. If you've been to the South Rim of the Grand Canyon, you might want to try the North Rim this time. Very nice and very different. If you have to choose between Zion and Bryce, see Bryce. More open , less crowded, unique landscape, and you can drive instead of riding a crowded trolley. Lots to choose from out there leaving from Denver or SLC also. We went north from Denver on our first trip and south on our second. Great trips!