We posed that question in last year's DCSki Survey, and again this year.
You can check out the results from last year at:
http://www.dcski.com/survey/results2003/index.phpTo weigh in with your own opinion, you can take this year's survey at:
http://www.dcski.com/survey/index.phpThe highest vote getters for "Best Terrain Park" last year were Snowshoe, Whitetail, Seven Springs, Wisp, Roundtop, and Massanutten.