Another reason I liked going East to West is that it saves the most spectacular scenery for last. I remember a day in Wyoming after crossing the plains of Minnesota and South Dakota, when we came up over a slight rise and around a bend in the road, and there were the Big Horns in the first snow of the fall. It was relly awesome and we all stopped to appreciate it.
I think one of the great sights in America is seeing the Rockies rise out of the plains.