Here is some info and a thread we started last year on the Icons
http://www.fordraptorforum.com/f40/icon-suspension-@-sdhq-4903/
All three of the big brands have some differences that go deeper than just the a color choice. I'm sure more can be added to these pros & cons.. But these are a good start..
Icon Pros-
Icon has a compression adjuster for fine tuning the ride
Full size 3” piston. This is the main piston that operates the entire stroke of the shock
Position sensitive - An additional internal bump shock for the last 3” of travel to control bottoming and kicking. This bump shock is split into (2) 1.5” zones, when combined with the damping of the main piston this gives 3 zones in both compression and rebound all with unique characteristics appropriate for that range of travel
Unlike an internal or most external bypass shocks that starts with overly stiff piston valving then "defeat" the piston by "Bypassing" fluid trough a hole or pop off valve the ICON system creates position sensitive control by adding piston area when force is needed rather than subtracting from an overworked small piston to make ride tolerable. In bottoming zones the ICON system has 119% more working piston area than an internal bypass and 49% more in the ride zone
Digressive rebound - The main 3” piston incorporates digressive piston geometry. This allows the shocks to have better low speed control without compromising high speed flow. this creates better stability in a fast lane change type of maneuver and quicker chassis recovery from large hits.
Icon Cons-
Currently the RCV axles do not work with them - Icon is working on a new lower cup
Icon does not make shocks for your trophy truck.. yet
King Pros-
Has a compression adjuster that affects the entire range of travel
Full size 3" Piston
King Cons-
Not position sensitive
Adds compression via the adjuster to prevent bottoming which in turns adds harshness to the ride zone
Trying to create enough force to resist bottoming from a compression adjuster that works on shaft displacement (as do most all variants of external compression adjusters) is problematic and is best used to supplement the overall tuning by 20-30%
Fox pros-
Has multiple internal zones for position sensitivity
Fox Cons-
No compression adjuster to adjust ride.
Internal position shocks use a smaller internal cylinder with bypass holes so the actual piston is only 2.5” (OE Fox is 2.5” body with a 2.0” piston)
Bypassing holes in inner can inherently have poor low speed control