Snowworld Landgraaf has imo the best park. However, you should also take a look at Snowworld Zoetermeer, Skidome Ruchpen, Skidome Terneuzen and snowcenter montana. There is also a freeski team in Belgium, snowvalley Peer (
http://www.airborneski.be/). Hopefully you have a car and don't live far from all these places like I do xD