Which one is the better internal art?
The only person who practiced the full 9 Yin is Guo Jing**.
The only person who practiced the full 9 Yang is Zhang Wuji**. However Zhang Wuji received a special internal boost in the qiankun bag. So we are unable to measure how good he was with 9 Yang alone.
However, we do know that Zhang Sanfeng got roughly 1/3 of 9 Yang. At age 110, Zhang Sanfeng is estimated to be roughly equal to ROCH Guo Jing in terms of internal cultivation.
Can we draw any conclusions from this?
**Other than the creators of these arts, obviously.