Which plugs are best for performance?

As a Mopar Partsman, I can tell you that your old Mopar came with Champions. My experience tells me to stick with the Champions. I've seen far to many cars puke up anything other than what Mopar sent the cars out with. As for the folks who swear by the NGK's, I think it's mental. Both brands are distributed by Federal-Mogul and the NGK line is primarily an import line. However with the heavy use of Mercedes designed engines in newer Mopar's you will see NGK's used a bit.
The only time I would ever suggest the use of the platinum or iridium plugs over copper core is for longevity reasons. When you have to remove a intake plenum and most of the upper engine to replace plugs, you don't want to do it every 30 to 60 thousand miles. Copper is a far better conductor, they just wear out faster because of that fact.
In the end, it's your car and do what you want.