Hello First of all, remembering that there is no point in being the best spirit if you do not have the ability to use it.
A list of the exact ranks has not yet been released. We have estimates of the strongest I will list a few: Holy Angel, Clear Sky Hammer, Radiant Holy Dragon, Darkness Holy Dragon, Tyrante purple Dragon, Seven (Nine) Treasure Glazed Tile Pagoda, Mountain Dragon King (but it may not be a soul spirit, it was poorly explained in the story), the spirits of Huo Youhao (Spirit Eyes, Ice Scorpion Emperor, Necromancer), Radiant phoenix, Atlas Lance, Fire Fenix, Blue Silver Emperor
Now we have 2 that I don't know if I consider spirit or lineage but in the wiki it says spirit: Tang Wullin (son of Tang San) Golden dragon king. Gu Yuena (Wife of Tang Wullin) Silver dragon king.
And finally what I find most appealing. (Purely my opinion) Tang / Lan Xuanyu (Son of Wullin + yuena), are two spirits Golden pattern Blue Silver and Silver pattern Blue Silver.
I hope it looks good, I don't speak English and I'm using the Google translator (^^), see you later.