Great writeup, musicman! Cheers!The best for loading soap would be SOC Mistura and Semogue Barbear Português Limited Edition 2023.
But honestly, I'm only saving a few seconds over my other brushes.
If we're talking about making lather I have quite a few favorites, including a Wald synthetic and SOC TNE LE boar - so I find no particular advantage to badger, boar or synthetic as a class of brush, although given my current collection I'd pick badger if forced to name a favorite.
There is no perfect brush for me. I like a fair amount of backbone - but not too much, and definitely soft tips - which can be diametrically opposed to the whole backbone thing, and a comfortable handle - pretty would be nice, and I really like a brush that doesn't like to fling soap around the bathroom. All my favorites are very close, with slight variations on each of my desired characteristics. Fortunately, I've learned to live without perfection - pretty darn good gets me by.