I have been to Sedona and the National parks in the area of St. George. Both areas offer great hiking, camping, and sight seeing.
When we went to Sedona, we rented a SUV at the Phoenix airport and continued to Prescott, spent a couple of days in the Prescott area. Took in some of the attractions in the Prescott area and I play golf one afternoon. Then we traveled to Jerome to Sedona, Oak Canyon, and the cliff dwellings of the Sinagua people. It was in the fall of the year so the weather was really great. Sedona, Oak Canyon, etc., are all a considerable contrast to the arid desert terrain of the area which enhances their natural beauty. During our stay we traveled up to Flagstaff for one day before returning to Phoenix for our return trip home. All beautiful, but simply not the spectacular contrast and beauty of the Utah National Parks.
Our time in Utah started by flying into Vegas. We did not stay in Vegas, been there and done that in the past. Traveled to St. George, enjoyed a day to rest and some fine dining. Then we traveled to Zion taking in a ghost town (rented SUV in Vegas) prior to getting to the park. Btw, I have a senior pass to the national parks - saves money and makes it easy to go in and out as you don't worry about fees. We spent several days in Zion National Park staying in St. George a couple of days and Springdale our last day prior to going to Bryce. The bus service gets you around and allows for a number of easy hikes. My wife has had knee replacement surgery so we avoided the difficult trails, but they abound. In this park you are basically in the valley and the cliffs and mountains tower above you. Definitely take the car through the park - it is a spectacular experience. We drove up in the morning of one day, took a picnic lunch with us to enjoy with a few short hikes, and drove back from the far end of the park in the afternoon. It was a beautiful day and memorable day trip. A couple of days were spent using the bus service, getting off at different points, museum in the park, hiking, relaxing and enjoying the dramatic scenery of the park. Then we proceeded to Bryce National Park. Bryce is just the opposite of Zion, you are on the rim and looking down at various viewpoints to the spectacular scenery below. We did this in one day and again planned ahead taking a large picnic basket - food and drinks with us. That night we traveled back to Vegas, actually stayed in Henderson, spent the next morning at the Hoover Dam and caught our flight home late afternoon. Again we were there in the fall of the year. The weather in St. George was in the 90's cooler in Zion, but when we visited Bryce National Park I was glad we had packed some layers for colder weather. It was cloudy and cold in the morning, sunny in the afternoon, but with a stiff cold breeze. Bryce gets close to the 8,000 mark in altitude. Another trip you can take in this area is to also visit the North Rim of the Grand Canyon. We passed on this because we have been to both the North and South rims of the Canyon in the past.
My wife's idea of camping is the Hilton, but if you plan to do any camping Zion is beautiful. I don't know how easy it is to make reservations, especially in the summer months. We tend to take such trips shortly after school is back in session.
This past year we took in San Diego, Mission Bay (5 days) and from there up to the Oregon Coast (around Astoria) for the second leg of our fall trip - 2017.