Should I take Hwy 70 to 89-- or Highway 20 to 89 In Utah??

I don't see any advantage to taking 15 to 70. We usually take 20 to get from 15 to 89. We often take 9 thru Zion for a change in scenery. For shorter grades, 9/59/389 via Hurricane, Fredonia and Kanab is another option.