4-2-1 increases torque in mid range RPMs mostly and 4-1 increases torque in the high end RPMs mostly.

If you're just looking for numbers then 4-1 would give you a bigger increase in horsepower since the torque gain is higher in the RPMs.

Both are good.

You should probably go with 4-1 if you frequently visit redline, or 4-2-1 if you want the power increase to be there without having to push your car that hard.

I myself have a DC SS 4-2-1 header.

P.S. Someone tell me if I'm way off here, I don't like giving people misinformation