for the alps, the timing of when you want to go really dictates where you'll be able to go, as the summer parks are open at differing times and to different extents
for example, most austrian parks close late may/early june, and then reopen in late aug or early sept (except hintertux). Zermatt is open year round, but their park isnt, Saas fee is closed until early july, and the frech parks are generally the same
Where are you coming from? Be aware that parks in europe generally aren't as good as those in north america, even at the mega resorts. I'm from canada, but live in switzerland now, and i generally find the parks weak compared to what i skied at home. Other people may argue, but you won't find the same mega features and plethora of rails you'll get during the winter at home.
In addition, the mountain towns in europe are generally quieter during the summer months, so if you're looking for apres etc, better off saving your money and coming during the winter