Hello and welcome.
Perhaps you can find some interesting discussion in this extensive topic:
For the nth time, How would you rank the Greats?
It's not easy to rank the Greats, but here are a few things that we do know (either stated or demonstrated):
Pre-16 years:
-Yang Guo with Heavy Iron Sword was said to be at a level similar to Demonic Swordsman Dugu Qiubai with Heavy Iron Sword
-Guo Jing =~ Golden Wheel Monk in the field of martial arts, but Guo Jing was a better fighter
-Hong Qigong and Ouyang Feng were both described to have improved their skills considerably since the end of LOCH
-Qiu Qianren was defeated by Yang Guo's Heavy Iron Sword
-Hong Qigong and Ouyang's internal energy was not less than that of Golden Wheel Monk
-Lin Chaoying was said to be better than the Greats at *some* point.
Post-16 years:
-Golden Wheel Monk's internal energy roughly doubled, his power increased greatly. It was mentioned by Jin Yong twice that he only dared step into the Mainland after 16 years because he had reached a level where he was confident about being able to defeat the combined forces of Pre-16 years Yang Guo and Little Dragon Girl
-The remaining old Greats--Huang, Yideng, and Zhou--were able to match GWM's power for a while, although GWM was superior to Yideng and would have eventually won
-Golden Wheel Monk fatally injured Qiu Qianren after an entire day of combat. However, at the time GWM had
NOT reached the 10th level of Dragon Elephant Prajna. When he faced Zhou Botong in chapter 38, he would have been more powerful than when he fought Qiu Qianren.
-Yang Guo at his normal level (non-sad) is still slightly better than GWM
-Yang Guo did not seem to master the wooden sword stage yet, whereas Demonic Swordsman progressed further into "overcoming the sword without a sword"
With that, here is how I would rank them:
1. (Demonic Swordsman Dugu Qiubai)
2. (Huang Shang, creator of "9 Yin"), Guo Jing, Yang Guo
3. Zhou Botong, Golden Wheel Monk
4. Eastern Heretic Huang Yaoshi, Southern Emperor Yideng, (Central Divinity Wang Chong Yang)
5. Qiu Qianren
6. (Lin Chaoying)
7. Hong Qigong, Ouyang Feng