Kakashi is kind of an elitest. So, Sasuke fit his mold of a perfect, genius, ninja, like himself. Naruto was like Gai, unpredictable and outgoing. So, Kakashi didn't take Naruto seriously, until Sasuke left.
I'd have to say any civillians, since they have no kind of training, or power.
As for weakest ninja, the kid with the runny nose that hangs with Konohamaru I would guess.
The two have been compare at least a few times. But, I just wondered, which do you think is more dangerous & more cunning, from what you've seen in the manga? And,if the two ever faught, who do think whould be the victor?