Darth Nihilus (prime) vs Vitiate (novel)

all-out

Nihilus tbh unless you believe Vitiate could nom entire planets on the fly like Nihilus, which from what I've seen there isn't much to support that.

Nihilus speak.

Vitiate without prep would be woefully outclassed.
With a bunch of rituals he could definitely win

There are techniques within the Force against which (in those pathetic times) there is no defense

So, Nihilus possibly Force pushes him to the death.