Need to change spark plugs in my 1997 E420. There are so many different kinds. What are the differences between plug types if I want to upgrade from the standard OEM? Is it worth the difference in price? Standard OEM is 2 dollars and some are 8 dollars.

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Norm K.
'97 E420 Sport
'06 E350 Sedan
'67 Mustang Coupe
'70 F-250
'15 VW Jetta