I skied Snowmass for a week this past season from April 5th - April 11th and had a great time. It was very uncrowded-some runs were literally empty. Plenty of manageable intermediate runs. There was more than adequate coverage (it even snowed one day).
They have some nice ski in/out accommodations, and the prices are greatly reduced in April.
You also have the option of going to Aspen to get more variety, but Snowmass has plenty to keep you busy for a week.