I've always had good luck with Autolite plugs. I have them in my '71 383 and my '70 351W. Both of those engines had Champions when I got them. I didn't change out the Champions right away, but when I got around to doing my first plug change I bought Autolites. My 390 was another story. That engine just never ran quite right with Champions, so I installed Accel U-Grooves (the yellow ones) and wow, what a difference! It was like night and day. They don't make those plugs anymore. I was so impressed with the Accel plugs, I went back and bought their coil. Next time I may use Autolites in it or try NGK. A friend of mine swears by NGK. Funny thing is, I have never tried Motorcraft plugs.
I started to not care for Champions when I had my first car, a '63 Chevy with a 6 cyl. I replaced all of them with new Champions, but the next time I tried a different brand. Without making any other changes, I noticed an improvement in the way it ran and felt.
After that, I even changed the Champion in my then new snowblower to an Autolite plug. I cranked the engine with the plug connected, but not in the cylinder just to look at the spark. Both plugs were brand new and gapped properly. The Champion made a dull yellow spark, while the Autolite made a bright blue spark. The Autolite was the direct, cross referenced replacement for the Champion. That was enough for me.
I don't know what it's like everywhere else, but around here Champions seem to be the lowest priced plugs. I think that may be why they are in so many used engines. Just my own personal experience.
