Mount snow definatly does not have the best park on the east coast....as for the east coast....
Best backcountry is going to be up north...Jay, Stowem Smuggs, Mad River, etc
Best park is probably okemo, loon, very debatable as many places have really solid features all depends on the layout and how much you can hit down the mountain.
Best groomers: Stratton. Never have skied groomers as nice anywhere besides deer valey