what do you mean by freeski? and boxes do damage the same as rails... neither are good for skis.
invaders are park specific, while chronics are park/all mtn. i have a pair of both, and if i was gonna ride park 100% of the time, id probably choose invaders.
however, for big kickers, and pipe, chronics are sick. somewhat stiff, so they pop well, and dont wash out. invaders are a really soft ski.