Is One Better Than The Other & Why?

Think what in part quench is doing... then you'll come to the conclusion that a piston with a dish/D cup that's either zero deck or step headed is best 'depending on chamber'. As said in a round about way..the piston makes more diff than open or closed chamber when mostly the plug side is the same. It's just simpler to flat top and closed chamber the build than it is to fiddle chambers and measure/mill piston quench pads. Weight/ grams of ea. are some other deciding factors in the trade for this or that.