Most newer cars use the Platinum plugs. Better is subjective. The difference between the three types are how long they wear and last. Copper being 30-60K, Platinum around 100K and Iridium longer. Of the course the costs reflects that.
Sometimes cars don't like the platinum plugs. How old is the car and what model? If it has a larger engine say like in a Jeep 6 or 8 cylinder then use the platinum. Smaller older cars do better with copper plugs. Have owned both so I just go with the engine size and the age. Just my 2 cents.
Double platinum plugs can last a 100k miles but not the single platinum plugs.
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