The ones that make the rifle go "BOOM" . Don't really think there is a "Best" primer. The one that works with your powder charge and makes it go off every time. I know from my rifles that Federal Fusion 209 primers work with Pyrodex RS while CCI 209 primers work with BH 209 for the most reliable loads for my rifles. As mentioned the BH 209 needs a hotter primer to use it along with the right type or style of breech plug for it.