Best level 6 unit.

A duel is not being considered here, only individual units...

Well, it's hard to say, since the thread didn't specify any criteria for evaluating one unit or another. I'm simply saying that one-on-one, Nagas are obviously stronger.
And as for the abilities: Knight damage = 15-30, so even with double damage of 15, their damage and the Nagas' is the same; the curse doesn't work, and as for the double damage, to kill them it would have to trigger every third turn, which is just...

Added after 2 minutes

I checked as well—the Naga wins... both the regular one and the Queen... and I thought the Knight was the strongest...

Now, regarding the regular Naga — I wouldn't be so sure, because agree that in this case, the turn priority will definitely belong to the "black death horses," and the first strike means a lot ;)