I just bought a set of Bosch - I think they are all close to the same. Ironically I pulled a set of NGK BMW marked plugs (out of my late N52) which although worn made 60k miles without a miss.
I was reading somewhere about tuning the N54 and someone who seemed quite knowledgeable was saying that the NGK Iridium plugs were better in the tuned engine (but needed to be gapped slightly differently in that scenario)
