For Park scene, for sure Laax! each year they build the best park in Switzerland + the Pipe, for the european Open, so that is prob first pick, also Davos has a nice pipe, not quite sure about the set up for the park. any way they are not too far one from each other, and also you need to have in Mind Corvatsch (close to st moritz) has a very good park specially at the end of the season after the Slopestyle World cup, and also a good pipe, the good thing is that you have a very good place to ski powder as well...
any doubts message me... i ski at corvatsch most of the time