In the past it probably would be "Powder Whore" from all the different powders I've tried (and still have partially used containers on my powder shelf...).
But after years of chronographing different loads, I seem to be settling on VihtaVuori N320, N340, 3N37, and N110 for all my handgun needs. They just meter so well out of my Lee Pro Auto-Disk, burn clean, with low ES and SD numbers. I wish they didn't cost so much, but that's life...