We get asked the same question regularly - which is the better manufacturer - Champion or NGK, generally the problem lies with modern plugs and this is our thoughts.
If the engine hasn't started straight away you will probably have wet the spark plugs up. Once the spark plugs have been coated on the inside there is a possibility that an additive which has already been added by the manufacturer to unleaded petrol causes the spark to track down to earth. Even with wire brushing and trying to burn it off it will carry on doing so. We have been told cleaning with oven cleaner does help but we have not tried this.

A good tip when replacing new plugs is to have your engine already started and warm first on the old plugs, then put your new plugs in. The highest resistance with the spark is when the plug is new and unused.

There is no technical report on this but selling plugs for 30 years these are our conclusions.

Also Donald Mckinsey has written about it in the United States and here are his thoughts on the problem
Donald Mckinsey

Are you having problems finding a spark plug that lasts very long in your old engines?

First let's define the problem with the new spark plugs. When the automobiles became controlled by computer, the spark plugs did not have to have the bottom of the insulator glazed. The cars have fuel injection and the computer will not put enough gasoline into the cylinder to flood it. It injects fuel into the cylinder and says I will not put any more fuel into the engine until it fires. Then it fires the cylinder with 4O,OOO volts, if something happens to this computer control and too much fuel is injected into the cylinder, and the engine floods, this vehicle will not run right until you have taken the old plugs out and replaced them with a new set. What has happened is the trash gasoline the Federal Government has forced on us has contaminated the spark plugs because they are not glazed on the bottom. However when was the last time you flooded a computer controlled vehicle? More than likely, never.

Now these old engines do not have computer control and if your carburetor is running rich or you flood the engine, the same thing happens. The bottom of the insulator where it fires the engine becomes contaminated and becomes junk. The point coil or magneto ignition does not have 4O,OOO volts to fire the spark plug.

The solution to this problem is to find the spark plugs that were manufactured prior to the time that they quit glazing the bottom of the insulator. (Around 1975-77..) In those engines that used 1/2" pipe thread spark plugs or 7/8 - 18 thread spark plugs, the best deal is to try to buy spark plugs that come apart so the insulator can be taken out and cleaned with WD-4O, kerosene, Diesel fuel, or other things that will not remove the glaze on the bottom of the insulator. In any case, do not sand blast or glass bead them. This removes the glaze and you have a short life plug just as though you had purchased one of the newly manufactured spark plugs.

Those plugs that do not come apart, but are glazed on the bottom of the insulator can be put in a can of the same material mentioned above and set over night. Then brush the carbon and oil out of them with an acid brush or other small brush. After cleaning them, blow them off to remove the excess cleaning liquid and you are ready to run again.

I cannot emphasize enough that spark plugs should not be sandblasted or glass beaded. Also that to get any length of life in the old engines, they must have an insulator that was glazed on the bottom.