Guessing by the info you gave, especially where you live, I would take the AR7 because its all regular(positive) camber and will really bite into that icy snow. The Alpha will give you more of a buttery feel with the rocker in the tip and tail. Personally I think the AR7 will hold an edge better and will be better for you but if you're really getting into dicking around in the park on every feature and want to give rocker park skis a try then go ahead and get them.
Both are awesome skis, but my vote goes to the AR7