Loved Utah when I visited six years ago. Was there for five nights, which was enough for the following itinerary.
Day 1: Land in Salt Lake. Go to March Madness games and watch Harvard upset New Mexico.
Day 2: 4 hr Drive to Bryce Canyon and stayed in Bryce Canyon Best Western. Hiked most of the day.
Day 3: Hit up Coral Sand Dunes near Bryce Canyon en route to Hurricane, Utah. Ate good Mexican food in a restaurant that was in the family's house
Day 4: Hit up Zion, hiked Angel's Landing (go early), rested and checked out other parts of the park.
Day 5: Morning in Zion and then drive up to SLC for the night. Spent time checking out Utah University, drive around, watch March Madness in restaurants drinking watered down beer.
Day 6: Fly back.
I'd love to go back again, especially since I missed the Southeastern part of the state (Moab, Arches)