Itachi.
Itachi has already bested kakashi in CQC (although you could argue that kakashi intended to get caught) and Kakashi can barely keep up with Itachi's seal forming speed or shuriken jutsu.
There's no CQC in the Narutoverse.
You're referring to H2H, of which in a direct confrontation, Kakashi did intend to get caught, so Naruto could land his Odama Rasengan.
In this scenario, there is no Sharingan. And because Itachi has always relied on the Sharingan whereas Kakashi prefers to use it only when it's absolutely necessary, the former is at a disadvantage.
I agree that Kakashi won't be able to keep up with Itachi's handseals but at the same time, I believe that the same would go for Itachi under these conditions, as Kakashi's handseals have also been noted for their speed.
Working in Itachi's favour, there is finger genjutsu but even if it that did work, it wouldn't be enough alone.
Plus, if this is War Arc Kakashi, then stamina also plays in his favour alongside the advantage of having the ability to counter any nature that Itachi could use (Water > Fire, Earth > Water etc).
In the end, I think this comes down to stamina. Kakashi has much more battle experience and a better stamina nowadays and I think the differences in skill in Base Form are trivial.
I'd give this to Kakashi high-diff purely because he won't be able take Itachi down until he's exhausted and vice-versa.
