If you're wondering what the difference is between The BCY cord, I'm not an expert on their material, but according to the info I've seen, BCY #23 is 1.6mm cord that is "covered" wtih SPECTRA.
"Spectra fiber is one of the world's strongest and lightest fibers. A bright white polyethylene, it is, pound-for-pound, ten times stronger than steel, more durable than polyester and has a specific strength that is 40 percent greater than aramid fiber.
So I guess #23 would be the most durable if the above is true. BCY's Description of #23 states "Spectra covered, highly durable". I can't tell you exactly what Spectra "covered" means as far as how it is covered and how much spectra is used.
Their D Braid is also 1.6mm braided Polyester.
Their #24 is 2.0mm braided Polyester, so it's a bit larger and stiffer than Their #23 or D Braid.
I believe their D Braid is pretty much the same as 1.6mm Mini-Blind Cord. I haven't tried the 1.6mm Mini-Blind cord, but the 1.8mm is just right for my taste.