i say naruto mid difficulty, he has sagemode, which gives him unlimited chakra supply. but it will be very tough since kakashi is smart and has alot of jutsus up his sleeve.
So, Kakashi was a jounin at a very young age without the sharingan..Along with a lot of jutsu added onto that.
And Naruto has the Sage Mode.
I'd have to go with Kakashi.