That's like asking a NASCAR fan what's more important to winning a race, the car or the driver?
If some cars are better, then the driver doesn't matter so much.
But if all cars are pretty much the same, then the driver makes a difference.
Because of all of the variables, then the real answer may be neither. It could be the engineers and workers who build the quality into each individual gun and load components.
There's nothing quite like the "scientific" method. Shoot a match and see how you, the gun and the load components actually perform.