Qualty pistons, you can't go wrong with either. Icon are the forged piston like from the parent company that also makes Keith Black pistons and their replacement piston line is Silvolite. SRP is the less expensive line from JE pistons.
Material choice is probably the biggest difference. Are you going to spray NOS or turbocharge or supercharge? The 2618 is stronger. It also expands more per degree. If the engine is going to be street driven mostly with some racing thrown in, but no NOS, then the SRP 4032 gets the nod. Because the alloy doesn't expand as much as the 2618, the piston to wall clearances can be set up tighter and decrease the amount of piston slap upon cold startup. If you think piston slap doesn't matter, check out the thousands maybe millions of vehicles serviced by chevy dealers when the first LS engines came out with pressed pins. Yup, piston slap caused GM to change the design to a floating pin, at some cost to the management. Other brands have experienced similar events.

Seriously, 21 grams difference is unnoticeable. You can buy the Icon 118 gram pins separately, they are also 2.750" long so they should fit with no hiccups.