Which one is better, the 9-shaped ring descender or the 8-shaped ring descender?

The 8-word ring is good.

The 8-shaped ring may be the most famous type of descender. Every company produces at least one type, and there is not much difference between all products. Figure 8 rings have a particularly wide range of uses, depending on what kind of rope is used and how much functionality is required, using the principle of friction to achieve protection.

The first and most common method is to pass the rope through one ring and then out of another ring (Figure A below);

The second most common method is to pass the rope through one ring. Insert it into the ring and lock it directly with the main lock (quick position) (Picture B below), protection principle;