Three very different skis.
Chronics:
Chronic (85ish underfoot) or chronic kryptonite (92ish underfoot)?
Both are very versatile park skis. Good durability, really nice stiff flex, awesome park skis. Great for big jumps, rails, and all-mountain.
Ledges:
Really durable, symmetrical shape, soft flex. Their more of a beginner park ski but their awesome on rails and small jumps. Super poppy, buttery feel, light weight.
I had them for 2 years and loved them, still in mint condition after two seasons of abuse.
AR7's:
Similar to old Chronics. Stiff flex, versatile, durable, pretty much your standard park sticks. Good on bigger jumps and rails.
How much do you weigh, how tall are you, what kind of flex do you like, where are you planning on mounting your skis, how good a skier are you (park and all-mountain)?