^^ Those are copper. I've read they're best for performance but need to be replaced more often than platinum.
I use NGK BKR6E which is the single prong (BKR6EK is the double prong). I think either is fine.
1998 BMW 328is - summer
1993 BMW 525i - daily
1994 BMW 325i - sold
1992 BMW 325i - gone
1988 Mercedes Benz 190E 2.3-8V - sold