Been to all these parks a number of times. Some observations:
It can be hot in Zion and Moab in both early June and early September.
With more hours of daylight in June, you'll be able to do more exploring.
I think Zion and Arches are both great hiking parks. We've done all the trails into Bryce and have to say that once you've done one loop, the others all have a ring of familiarity to them. We tend to stay in Zion twice as long as we stay at Bryce.
If you go to Zion, plan your hiking around the sun. Hike those trails on the east side of the canyon in the morning when they are in the shade and those on the west side of the canyon in the afternoon when they are in the shade. In the middle of the day, hang out around the Virgin River, maybe take your shoes off and wade. Do plan on taking one day to hike up Zion Narrows. It's cool in there even on the hottest days in the summer. On the east side, take the trail above Weeping Rock to Hidden Canyon. When you get to the sign that says end of trail, keep going. The first part is easy walking. You can get pretty far up with some easy scrambling. Go until you're intimidated and turn around. Hidden Canyon is narrow and stays cooler.
At Arches, there are a good variety of trails. Of course most involve arches, but the setting can be so different. If you have the stamina, take the Devil's Garden trail out to at least Double O arch and return via the primitive loop trail. Great fun and it gets you away from some of the crowds. Book a guided hike into Fiery Furnace. Take one late afternoon hike to Delicate Arch to watch the sunset. The red rocks with the LaSal Mountains in the background are just spectacular. Just in case you tarry a little long, take a flashlight to return. You won't be the only one out there, but it's still an amazing experience.
Island in the Sky at Canyonlands has several view points to check out with access trails of varying length. Not much in the way of longer hikes that I could recommend, but the drive is worth the view. On your return to Moab, head down Shafer Trail and back into town along the north bank of the river. This is a graded dirt road with a few places to look out for, but I did it in a 1981 Honda Accord way back when (not 4x4). Just a different experience to go back that way.
One hike that's outside the park that can be nice in the heat of the day in Negro Bill Canyon. It start about three miles up UT 128 from US 191. This is a fairly narrow canyon with a perennial stream. At the end is Morning Glory Arch.
As you can see, I can't really answer your question as to which is more spectacular. But at least I've given you ideas of hikes to do when you do get there.