In my mind, the two most devastating abilities Dark Side users have ever produced.
But, which overall, do you think is preferable?
Palpatine’s Force Storm
"Using this knowledge, I can unleash the dark side energies that are all around us, even to shatter the fabric of space itself. In this way, I have created storms."
Sidious
Here, Palpatine employs the Storm to create a hyperspace wormhole from Byss that travels to Luke on Coruscant. Using this, Palpatine transports Luke to one of his ships.
He would later use the technique to destroy starships and was finally killed by losing control of it due to Luke and Leia covering him in the light side of the Force and preventing him from accessing the rage necessary to control the Storm.
Palpatine himself admits he can not completely control these awesome powers but canonically, he never lost control except from the direct intervention of Luke Skywalker himself somehow shielding him from the Dark Side.
Advantages of this technique are obviously distance. Lightyears can separate you and your foe and you can still destroy them. Also it comes with versatility as you can either move a target or annihilate it.
Nihilus’ Technique
“It is a technique that is almost as old as the Sith themselves... it is a means of severing connections between life, the Force, and feeding upon the death it causes.It cannot be taught... it can only be gained through instinct, through experiencing its effects, first-hand.{Quietly}Yes. And he fed upon its destruction - it will sustain him, for a time.Because it is not something that can ever truly be controlled... and it leaves nothing to conquer in its wake.And it rules him, not the other way around. It has its own will, its own instincts.”
This is the only canon world Nihilus destroyed; the planet of Katarr.
We are told there were at elast two Jedi Masters upon the planet by I believe Kavar. We know at the time of KOTOR II, there was less than 100 Jedi still alive. And Nihilus did not kill all of them on Katarr, I don’t think. So, we don’t have a real figure on how many Nihilus killed. Just the Jedi and Miraluka colony.
Like the Force Storm, this power can not be controlled. Nihilus is little more than a cancer in the Force because of it. But this techniqu eis obviously quick-acting with mass devastation. “When my lord spoke, all life on Katarr died.”
But in the end, it comes down tot his I feel:
Nihilus’ awesome power requires one thing to work: life/The Force. This power is worthless against anything non-living.
Palpatine’s Force Storm is indiscriminate and will wipe out anything. It has no special requirements about the target.
Thus, if Palpatine and Nihilus were left alone and cornered by a fleet of starships controlled by AI and they only had their most powerful move, then Nihilus is SOL. He can’t drain which doesn’t exist. Palpatine’s Force Storm, however, will wipe out those ships no sweat.
That’s my thoughts and I want to see what everyone else thinks.
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."
Nihilus abilities aren't even remotely as impressive as people make them out to be. It's a result of his condition and has very little to do with his personal power.