[quote=@Raijinslayer]
<Snipped quote by hatakekuro>

That's a good question. . . considering the varied skill sets of all of the servants. Nidhogg is definitely one of the higher ranks, as his Roots are both strong, durable, and versatile weapons and tools, and can even act on their own
[/quote]
I'm actually gonna say Huangdi matches Nidhogg here and probably beats him if the fight is in Huangdi's territory. I don't know what I'm going for in terms of personality restriction ( the guy is a benevolent ruler type), but it seems like Huangdi is medea tier which is really really good as a mage. His Gaia connection let's him spam phantasmal beasts like a dragon as much as he wants of course with the problem of him only being able to have one phantasmal beast.

On a side note, Eastern Dragons are capable of destroying the entire world in a rampage, but thankfully the grail can't summon them.