I used to go back and forth between 42's and 45's.  Couldn't tell the difference.  Can't remember what is in there now because I drive it so little that plugs never wear out.

IME copper plugs provide the best spark.  They fell out of favor because OEMs wanted to go to 100k tune ups, and copper plugs typically only go 30k or less.  This led to the widespread use of platinum plugs..  I've run stock replacement Autolite plugs for as long as I've owned my '67.  Never had an issue, and thus never saw a reason to change.

Rudi wrote:

A local offshore race engine builder told me to get rid of the platinum tipped Bosch plugs and use regular NGK Copper core spark plugs. That is the plug he uses in all his builds.

Yeah, all the fancy crapola plugs are, for the most part, marketing. When I worked in auto parts a long time ago I remember when Splitfire plugs came along charging 4x what a regular copper plug cost. People where all over them thinking they did everything including solving world hunger...

Good ol' copper plugs are all I run too!
 

That's true, BUT if the plug is the wrong heat range you will erode the electrode of those fine tipped plugs MUCH faster.  Iridium plugs are very spendy, though great for turbo applications, so long as you get the heat range right.  I used a stock heat range plug in my WRX and in 10k miles had all kinds of misfire codes.  I pulled the plugs and they had almost no tip left!  I went a heat range colder and the same plugs have been in it for 30k without issue.  I guess the tune is considerably hotter than stock and required a colder plug (no one told me that of course).