NGK Spark Plugs..

[PxTx]

I too have had good luck with NGK.

I have also done a bunch of research on how plugs are made. Champion is sort of unique in manufacturing. If you've got any laying around, you can actually unthread the metal plug connector form the porcelain. You can then see the talc, spring and resistor (or not depending). Kinda neat to see the anatomy of a spark plug.

I would suspect that if Champion is making AC plugs, they would be making them to AC spec, and not necessarily their own. I bet you can still unthread a Champion end, while the AC plugs probably are assembled as they always were. Not saying anything about the quality of the old vs new other than they are not equivalents of each other just because Champion makes both.