Suggestions:
Zion- Hikes, 1. The Narrows (must do) 2. Overlook trail (starts at the eastern entrance to the tunnel) 3. Angel's Landing (if you have the stomach, we didn't) We also did the Emerald Pools trails up to the upper pools. It was nice, but would cut it if short on time.
Arches- Hikes, 1. Devil's Garden 2. Really, every spot in the park is worth the time. Wish we could have done "Fiery Furnace", but we didn't realize it required reservations.
Canyonlands- We enjoyed our time there, but would skip this park entirely if you wanted to use a day elsewhere.
Bryce- Hike the Navajo to Queen's garden and come up through Wall Street. Of all the parks we went to, this is the one we wish we had done the horseback trails at.