Bryce Nat. Park, Glen Cyn. Nat. Rec. Area/ Badlands Nat. Pk.

I would base my choices on weather conditions at your possible destinations just before heading out.
I've been to Bryce in March and seen both snow, or deep red mud, on the trails into the canyon. If it's in a thaw situation there, you probably won't want to do much hiking on them. They're messy.
Badlands might be too far north in April. I have little experience there in early Spring.
Glen Canyon Rec Area might be your best bet. Lake Powell RA might be in good shape.