They are both awesome but the canyon has more from a geological perspective
Would You Rather Marvel at Australia's Ayer's Rock or Gape at the Grand Canyon?
While marvelling and gaping both have their charm, I'll give both a miss. I'd rather swim on the Great Barrier Reef. Magic place.
I'm partial to the grand canyon but you have to remember how huge it is. You really can't just look at one part and get a good look.