It comes down to your style in the park. Some professional rippers prefer the bigger based ski because of how it slows everything down and looks awesome (Pep, Andy Mahre, Pollard, etc.). A downside to using a fatty stick in the park is that if you're hitting a big jump (60ft.+), you'll notice a considerable drag on the skis caused just by the wind. It make make certain tricks very sketch to toss. As already mentioned, a bigger ski will be harder to toss spins on jumps and maneuver on rails but if simpler tricks are your game, you'll have less reason to object to using pow skis in the park. Mind you this is referring to skis with a waist width of 105mm+ minimum. Anything in the 90-100mm range, I would consider more of a true all mountain type ski and you'll have much less issues to worry about.
When I had Hellbents, I always tried bringing them into the park a few days out of the year. Its a completely different feel and its so much fun. You'll have a blast straight sliding and pressing on boxes and just doing simple floaty stuff off jumps. It also makes tranny finding much easier as they can plow over anything.