What exactly are you looking for - a place with great natural beauty?
All are beautiful in their own way if you appreciate desert landscapes.
That said, I'd be saving myself the several hours of driving and head to Red Rock Canyon. I've driven through or been to all three parks you mentioned and while they all have their own wonderful merits, I wouldn't necessarily put any of them so far ahead of Red Rock that it would be worth a 4, 5 hour round trip drive (or 8 in the case of Bryce). . Red Rock is only 25-30 minutes from the Vegas Strip without traffic.
I meant to add the info below but missed the edit window!
The National Parks in the Western U.S., especially in Utah and Wyoming, are nearly at max capacity 7 days a week. The Park Service is so overwhelmed at some parks that they are discussing the possibility of strict limits on the number of visitors per day to ensure the natural habitat and public safety is maintained.
Bryce, Zion, Arches and Canyonlands are four such parks (all in Utah) that are at near max capacity daily with visitors, especially in June, July, August. Visiting these parks at peak time can be downright miserable as significant sights are packed with tourists. I was just in Yellowstone last summer, a park I've been to a dozen times, and it was absolutely horrible.
I do not say this to scare you away from this day trips, but more to prepare and also in helping you decide whether it is worth spending an entire day traveling to national parks that might be overwhelmed with visitors is worth your time and money..
In a previous topic you wrote that you are going to Las Vegas "soon". Are you sure that the day tour provider you are considering even offers tours to DVNP during your visit?
Many operators do not offer tours during June, July, and August. Something to consider.
As far as how one park compares to the others, all three are quite different and have incredible scenery.
We've been to all three, but never on a bus tour. Since DVNP is so large, the various points of interest are spread out. It would be easier to 'pass through' ZNP or BCNP using their shuttle systems. Certainly not for me, however many people visit those parks in that manner.
Downola has given you some very practical advice and things to consider.
We have visited all three, and find all three to be beautiful
Take your pick. They're all beautiful but in different ways. Of the three, Bryce is our favorite because of the unworldy hoodoo landscape but it is also a long drive. I would be reluctant to go to DV in the summer. To me, the heat is unbearable and downright dangerous if you spend any time outside. Zion is also beautiful but, as mentioned, in the summer it is very crowded and you have to go on a shuttle through the park but you can get off and on at various stops. Sometimes the lines for the shuttle are long and it may cut into your day. Don't know how that works with tour buses. Whatever you decide, it's almost always better to drive yourself and you're not on anyone else's schedule.
thanks to everyone for input, you guys on here are great.
Having visited a lot of the parks in California, Nevada, Arizona and Utah over many visits to Las Vegas from the UK - Bryce is my personal favourite. The views are stunning (better than the Grand Canyon IMO) and nothing like we have back home in the UK. Make the effort (pay the extra) and go on a Small Group Tour to Bryce. You will not be disappointed! Enjoy!
Just to add to the pot, I’ve been to all 3 and Zion is my favourite! It’s closer than Bryce,but what you would see in a day tour I’m not sure. You lose an hour going but gain it on the way back! Bryce is definitely different but is a long way to go in a day. Just looked on google maps, 2 1/2 hours to Zion 4 hours to Bryce and that’s in a car not a coach.