Bosch has that odd design that has the thin platinum center electrode buried flush in the insulator. Bosch always claimed that the platinum would resist erosion so well that it would self-clean. I heard in practice it didn't work so well.
I used to take my car to a Japanese car specialist shop. They used Denso plugs for almost anything, including where NGK was specified, as long as the Denso plug was properly cross-referenced. But what they told me was that they went with Bosch for years (their conventional plugs were actually quite good) - at least until their platinum plugs. They'd come back with the electrode having vaporized away.
I thought that it was telling that even German carmakers were going with Denso or NGK.
