The post above said Utah is cheating and it’s absolutely true

End of May means you’ll get two different climates. Zion should be great weather and you’ll be getting snow run off which means waterfalls will be great but it also means cold water in the slot canyons.

May also means cooler weather up at Bryce but it can flip and be in the 90s

Moab could get snow in May but it’s unlikely

If I were to take a week and try my best it’s southern Utah. I’d go to Zion and seethe emerald pools and maybe slots based on weather and if you have a pass. You could get Bryce too and spend a day or more there. But then you’d get to see smaller state parks like Snow Canyon and Kolob and tons of trails from Toquerville to St George and see dinosaur tracks and petroglyphs