SSS Tier:
- Post-rose Mereum (I maintain that even this form of Mereum cannot face the calamities and other even more powerful entities in DC, given what we've seen of Alluka as the gaseous life form Ai).
SS
Netero (weaker than pre-rose Mereum, undoubtedly, but I don't think anyone in the lower tiers can take on Netero), Pre-rose Mereum, Ging (& other top 4 nen users), Gon-san
S
Neferpitou, Menthuthuyoupi, Shaiapouf, Chrollo (not in terms of raw power, but in terms of Hatsu, intellect, and combat prowess)
A
Kite, Razor, Phantom Troupe (especially Feitan, Phinks, Nobunaga), Morel, Knov (he's cowardly, but still powerful)
B
Shoot, Knuckle, Palm, Captain-level Chimera Ants, Killua (given a bit more proficiency in Godspeed, then he'll shoot right into A tier; his Hatsu will be monstrous in his prime)
C
Gon (bottomless potential, but he started later than Killua and will face the issue of regaining his nen when and once he makes the trek to DC; the catalyst will probably be something happening to his dad in DC), Genthru (I think Gon post-invasion can take on Genthru no problem)