Well we have both, a 2014 Spark and a 2015 GTR.
After riding the Spark for one season we decided to buy another one so we could ride together. The Spark is a superfun playmachine and we are really satisfied with its performance but wanted to have a different second one so we could alternate between them.
The GTR is GREAT allaround ski, playfull, fast and comortable and if I had to choose one it would be the GTR.