The best load for self-defense is, the load you have with you when you need it most.
Basically, science has taught me that with handgun defensive loads, the best results are usually obtained using lighter bullets with hotter loads. For example, the so called "King of the Street" back in the 1970s was the .357 loaded with a 125 gr JHP. 125 gr is certainly at the lighter end of the scale for .357 bullets. Later we saw pretty good results using 9mm with 124 gr bullets. The success of those loads helped to propel the development of the .357 Sig load with the idea that lighter and faster obtained better results than heavy and slow. Personally, I use custom loads. For .40 S&W I use Nosler 135 gr JHPs with a powder charge sufficient to give a muzzle velocity of 1300 fps. For 10mm I use a Nosler 150 gr JHP at 1350 fps. For .45 ACP, I use Speer Gold Dot 185 gr bullets at 1050 fps and 200 gr bullets at 1000 fps. Those are just a few examples that can help you understand what I am talking about. So, to recap, basically look for hotter loads with lighter bullets.