In my opinion, mountains in Utah are one of the best ski destinations in the United States. Snowbird is great. There are cliffs, moguls, trees and many steep trails above the forest level. Taking the aerial tram to the top of Hidden Peak (3,300 m /11,000 ft.) allows for a continuous descent of vertical 950 m / 3,240 ft.
Ski trails in Alta are mostly short and not challenging. The whole resort is like for intermediate level skiers. There are only a few ski lifts here. Lack of modern development at the base makes Alta a place for a day-trip, not a resort where you could spend a winter holiday. The scenery is spectacular, but it does not compensate for other shortcomings.
Park City Mountain Resort is the largest skiing center in the United States. The area is huge. You need almost entire day to ski between two distinct base areas. There are slopes for everyone and plenty of challenging trails. The trail we loved most is the Abyss.