I haven't thrown a Storm in a while, but I believe it's the easy length and improved backend transition. Storm's several years ago were traditionally long and strong, when they hit friction, they went nuts. The transition has smoothed out, while still maintaining the easy length, meaning the pros can get a handful at the bottom and not worry about it moving early. This also means when the shot starts breaking down that they will get more subtle warning (ie, 4 pin instead of big 4), and should be able to hold a line longer than other stuff.
I've recently drilled a Yellow Pearl Misfit and Brutal Nightmare, and as far as DV8 goes, it's MUCH better on a tight fresh shot than other companies, there's an extra board or two to the right in the oil because of their backend transition, but everything seems to roll the same, just varies in hook potential. I also have a Motiv Sigma Tour, and although Motiv has a tendency to "stand up," the reaction is super clean. Storm has the most versatility in their lineup if you want to stay with one company. They have long and strong, early and smooth, somewhere in the middle, snappy pearls, smooth pearls, snappy solids, smooth solids, etc.