long and the short of it
copper plugs= cheaper, do the same job as the iridiums, foul quicker
Iridium plugs=expensive, do the same job as the coppers, more resistant to fouling.
That sed tho, depending on your tune, the iridiums can be useless as they will eventually foul. All comes down to how much you like changing your plugs and playing with ur coilpacks.
Me i prefer not to tocuh the coils as little as possible and therefore use the iridiums but each to his own.