I conducted accuracy tests with a variety of self-defense rounds using my M&P 40c (1.0). I started by choosing ammo that met FBI standards for penetration and expansion. The report on these rounds can be found here:
Self Defense Ammo
I shot at least 50 rounds of each brand I tested at a 4"x4" target at 20 yards and recorded the percentage of hits inside that square. I tested seven brands, but the one that stood out as the most accurate (from my gun at least) was Speer Gold Dot 180g. It was the only round that went into the 4"x4" square more than 50% of the time (it hit with 52% of my shots). In second place was Remington Golden Saber HPJ 180g, with a 47% hit rate. In third place was Winchester Ranger T 180g, with a 40% hit rate. Despite the significantly lower hit rate, the Ranger T grouped the best, with very few flyers. My 40c is my everyday carry, and I carry with the Gold Dots.
Of course my results are with my gun as fired by me. Your results may vary, so I suggest doing your own accuracy research. It's fun, and a good way to learn about your gun. It's also expensive, but what's your life worth?
Good shooting!