When I was young (can just about remember it!) Champion were the basic cheap plug from Halfrauds, if you wanted somehting better it was NGK or Bosch. I had a number of Vauxhalls and found they generally ran best on AC, or Motorcraft or all things. Having moved to Saabs some time back I switched to NGK as they are the only one that works properly with the Trionic DI ignition packs. I also started off the TR7 with NGK as they seemed to be recommended but had trouble with a couple of sets in both cars (or one in each set), then found that NGK are now made if France and don't seem to have the quality of the Japanese originals.
Alan
Saab 9000 Stg 1
Saab 9000 2.3 FPT Auto
'81 TR7 DHC