There are many factors.
Looking at the "mechanics" of it, "brand "x" may be more accurate than brand "y" in your paticular gun. But the opposite may be true for your neighbor with the same ruger. Each handgun is a different animal to its own as to what paticular load it likes the best for accuracy.
The best way i know of to determine it one round has superior accuracy would to to lock the gun into a rest, shoot single action, and at a "distance" of say 25 yds. This would take the human factor out of it and one could see if brand "x" or "y" shoots a tighter group.
But put the human factor in, pratically anything goes with variables such as recoil, flinch, blast, etc. Brand "x" may be the winner in accuracy from a machine rest at 25 yds, but due to the above factors, it may "pattern" instead of group at a shorter distance of 10 yds in human hands. While brand "y" shot a much better group at 10 yds in human hands---because of less recoil, flinch, etc.