Zion is a great place for big wall climbing, with massive 2,000 foot cliff faces overlooking the river-cut valley below. This location, like Yosemite and Joshua Tree, gets overrun with tourist during the summer, a time which isn't actually great for climbing because of the heat, so camping reservations are recommended. Also, in comparison to the other places listed, I would say Zion is best for more experienced climbers. Even if you don't climb though, camping in Zion and witnessing its beauty makes any trip there worthwhile.