just brand difference... some car companies prefer a certain brand over the other
Denso was the first manufacturer that came out with the Iridium design, and is regarded as the leading company. Many aftermarket specialists such as HKS are using Denso for their high performance plugs
NGK has been playing catch up with Denso, and also have the Iridium technology, but in order to conquer market share, their prices are lower than Denso.
Some people think that Denso are better than NGK .