If you want to go to Bryce and Grand Canyon (regardless of which rim) then Vegas is closer than Salt Lake City.

There's not enough to do at the Grand Canyon south rim for you to spend the entire time there if you fly into Phoenix.

A loop from Vegas to Zion, then Bryce, then North Rim and back to Vegas is about 14 hours of driving. Vegas to Zion - Bryce - South Rim and back to Vegas is 15.5 hours of driving.

It seems to me you will have enough time to go to Bryce and Grand Canyon and satisfy both of you. The only real question is north or south rim. Some people think sunrise/sunset is better at the north rim - there certainly will be fewer people. And it is cooler and quieter there. The issue is that you'd need to get lodging in the park for sure if you stay at the north rim as you don't want to drive all the way in/out for sunset and then sunrise. It's best to stay in park at the south rim too.

Right now there is no lodging available at the north rim for any of your dates. There is at the south rim.

In general I'd say it would be better to stay at the Grand Canyon on the 16th, then Bryce on the 17th and 2 nights at Zion on the 18th and 19th. That would mean you have the shortest possible drive back to Vegas on the 20th so less worries about traffic. However, that really depends heavily on your arrival/departure times on the 16th and 20th. It's 5-5.5 hours from Vegas to either rim, but around 3 hours from Vegas to Zion.

At this point, if you know your flight times, then your first order of business is to decide your route and start trying to get lodging booked. If you want to stay at the north rim, call them every day or twice a day as there are always cancellations. Make a reservation for the south rim in case nothing opens up on the north rim, and that can be your backup plan (or primary plan if you'd rather go to the south rim). Same goes for Zion and Bryce - if you want to stay in the park and there is no availability, call until you get something. Or there is lodging very close to both of them just outside the park.

Lodging for South Rim is:
http://www.grandcanyonlodges.com/

North Rim is:
http://grandcanyonforever.com/lodging/

Zion (in park) is:
http://www.zionlodge.com/

Bryce Canyon (in park) is:
http://brycecanyonforever.com/lodging/

I think flying into and out of Las Vegas is the wisest choice. Do those dates include travel days or are your flights on Aug 15 and 21? The main thing you must do right away is to secure lodging. These are popular parks.

We usually fly into Vegas, rent a car and drive directly to Zion (2 1/2 hours) or , if our flight is late, we drive to Mequite to overnight at the Best Western (not much else there unless you like a smoky casino) or in St. George where there are a number of options. But if you are not too tired and it's not too late, drive directly to Springdale. Keep in mind that few motels in Springdale have 24-hr or even late-night reception. Best Western does as does the lodge inside the park; I'm not sure about Desert Pearl.

In Zion we like to stay at the lodge inside the Zion Canyon (inside the national park). There are often cancellations, so keep calling Xanterra, the park concessionaire. We like to be close to the trails. There are many easy, casual walking options in all of these parks. If you do not stay inside the park, you cannot drive in, but must take the shuttle from the Visitor Center. The Desert Pearl Inn is a lovely option in town. The Best Western is comfortable enough.

Bryce is wonderful, and again you can chose relatively strolling walks or hike down the canyon a little. Try to stay in one of the cabins here if possible.

At North Rim Grand Canyon there are limited lodging options. You could stay outside the park in Kanab but it is still quite a drive in. At North Rim we had a motel room that was pretty dreadful and we regretted we'd booked 2 nights. But I understand the other lodging options are better there.

I'd develop the itinerary based on what lodging you can find, but we would choose Zion, Bryce then North Rim and back to Vegas for the flight home. Make your flight home as late as you can so you don't feel pressured to get to the airport. There can be bad traffic at times as you get closer to Vegas.

Hope it all works out for you. This is one of my favorite trips and we go to Zion every year.

You guys are so awesome! I just booked our trip and had to change it a little based on hotel availability at the Grand Canyon.

We are flying into Vegas on Thursday and arriving around noon. We'll drive to Zion, stay overnight there on Thursday and then the next day explore Zion. We'll then drive to Bryce Friday afternoon/evening, and we're staying at the Bryce Canyon Inn on Friday night. Saturday we will check out Bryce then head to the Grand Canyon, North Rim and we are staying at the lodge in the park (there was an opening!). We're only going to spend one night, see sunrise/sunset and then head back to Vegas on Sunday evening. We're going to stay at Green Valley Ranch in Vegas (get some relaxation/pool time before the flight home) and our flight is not until almost midnight on Monday evening!

Do either of you know about transportation to the North Rim view points? Will there be a shuttle from the lodge? We will obviously have a rental car and I've heard the roads can be rough and unpaved.

Thanks again for all the helpful advice!

I don't recall a shuttle at the north rim, but the roads certainly were not a problem when we were there. We had a rental car also. I wouldn't worry about it. I'm glad you were able to find lodging. Enjoy! ( I'm guessing you'll wish you had more time in each place).