Some spark plug brands seem to work better than other brands in some engines, by observation.
I started using NGK V-power plugs and discovered a sharper throttle response with that style of plug (which Toyota has used for many years, but with normal nomenclature on it). How much difference they make depends upon the combustion chamber design. They made a noticeable difference in my '80 Chrysler 360, but not quite so much in a '67 Chrysler 383 (w/906 heads) or in my '77 Camaro 305.
Check out the brochure for the new Autolite Iridium plugs. It shows some good shots of the flame kernel of these plugs (and some competitors' plugs too!) . . . which is really what it's all about.
I used to have Champions in all of our Chrysler products, as that's basically the "spec" plug for Chryslers. I now have NGKs in them and they work well too--at least as well as the higher priced Splitfires.
It might be all about just getting a spark to ignite the fuel/air mixture, but it's now important that the quality of the spark and its "fire" is more important than in the past. Not to mention how much of the original electrical energy gets "through" the plug to make the spark.
Enjoy!
CBODY67