Originally posted by Dolos
I'm honestly undecided.Who's knowledge was greater?
Vitiate had knowledge of the ancient Sith Lords themselves - perhaps the greatest source of Dark Side knowledge. A source lost to Bane, knowledge which DE Sidious could only piece together from centuries of excavation across countless and innumerable star systems to come to a total understanding after his death gave him time to make sense of it all. Sidious' knowledge perhaps rivaled Vitiate's when combined with the knowledge gained from Revan, Bane, and the millennia of increasingly deadly Sith Lords after him who had adhered to the Rule of Two.
Both Sidious and Vitiate were innately prodigious, Sidious was older when he started, yet he was still miraculously gifted given the limitations of his Force potential. The incredible things Vitiate did as a child prodigy could be attributed to his Force potential moreso than Palpatine's, whose abilities were more from his intellectual capability, whereas Vitiate's was more the result of his Dark Sith Blood. The result was that they both learned quicker than Anakin and even Luke - the most prodigious Jedi of all.
In the end, Palpatine gained a greater understanding of the Dark Side, and was more corrupted by it - on the basis that I can't see Vitiate summoning Great Rifts in space-time by tapping the Netherworld of the Dark Side, yet I can see Sidious performing the ritual of Nathema to increase his power and lifespan to nearly inexhaustible levels.
Sidious FTW.
P.S.
They both contain two incomplete chunks of esoteric Dark Side knowledge vast beyond imagining. If pieced together in the capable hands of a megalomaniac Force sensitive like Palpatine was, it could create a being capable of threatening The Ones and the galaxy more existentially than Abeloth herself.
This might help:
"In his relentless pursuit of immortality, the Emperor explored the most sinister, uncharted depths of the dark side." (SWTORE)
"Should he succeed in his plans, the Emperor will conquer death itself and become the most powerful being in all of galactic history." (SWTORE)
Some information here: http://www.swtor-spy.com/codex/the-emperors-plan-knight/324/
Sith Emperor had lot of time under his disposal to study the dark side and he eventually reached a point at which he could annihilate the entire galaxy after adequate preparation of-course; no other dark side practitioner in the known history of Star Wars posed this much threat to the galaxy itself; not even Abeloth.
With GL out of the picture and new content continuously pouring in to Star Wars mythos, we are left with subjective preferences in debates like these.
From neutral perspective, both Sidious and Vitiate are impressive in their own right in the grand picture. Both honed their talents in different manner; their preferences being influenced by their surroundings and circumstances. Both were extraordinarily powerful in the Force. Sidious is relatively much more explored character whereas much of the Vitiate's capabilities are shrouded in mystery and/or yet to be explored. However, Vitiate's story is panning out in more promising and exciting fashion and logic dictates that Vitiate became nearly reached the pinnacle of dark side practitioners but was stopped with combination of multitude of factors/forces working against him after his true nature came to light.