I visted Sun Valley the week before Christmas. I've read mixed reviews on the resort but I have to disagree with the negative ones.
The runs are long and the scenery on a clear day is magnificent. They were no lift lines, ski up to the lift and get right on.
The lift tickets were pricey and they considered a child an adult at age 13.
There is two sides of the mountain that you can board the lifts, river run and warm springs. We stayed on the river run side which the access to the lifts is to far to walk. They advertise across the street from the Best Western but its a good hike to lift. They have a free bus but it runs opposite of the lifts from the hotels that are close.
The warm springs side the hotels looked like they were alot closer to the lifts, where it was actually walking distance.