Spark plug selection

I run NGK plugs in all of my yard equipment even though they might call for champion plugs, they start better, perform better. When I had my '73 dart swinger with a 318 I ran Bosch mostly. My parents bought a new 5th Avenue and it ran rough at a idle, my dad had the dealership install Bosch platinum plugs and the rough idle went away. I'm not saying that champion plugs are junk, it's that I've never had any luck with them.