Hello
NGK is the best value buy. Bosch are high level and have some very special plugs but why buying Silverelectrode Bosch or Champion NG2´s for early 911 S when a standard NGK does perform good enough ?
However there are some applications where you have only Bosch or only NGK to cover.
May favorite spark plug companys are NGK, Champion followed by Bosch, Beru. However on some Alfas ypu still can´t substitude the Golden Lodges
Grüsse