Why I think Palpatine would win
Palpatine's power:
Before I start, I just want to say that canon Palpatine loses, there's no way around that, however for there to be any kind of debate and stopping this from being a total mismatch, I'll be assessing Legends Palpatine.
Palpatine is an extremely powerful individual, stated to be the most powerful Sith in Galactic history. This includes the likes of Darth Nihilus, who could drain entire planets effortlessly. This also includes other old ancient Sith, such as Tulak Hord, Naga Sadow and Exar Kun. This would also mean he's more powerful than Emperor Vitiate.
Inside the spacious interior of the Galactic Senate chamber, Yoda challenged the Emperor. The two engaged in a spectacular duel—a contest between the most powerful practitioners of the Force’s light and dark sides.
- Source: The Complete Star Wars Encyclopedia
It quickly became clear to Luke that this decrepit and seemingly defenseless old man was masterfully adept in the ways of the Dark Side of the Force. Indeed, as Vader had warned, the Emperor had become the Dark Side's most powerful expression.
- Source: Dark Empire endnotes
It's been stated that Palpatine knew almost everything about the force.
Palpatine has spent decades studying the most arcane and esoteric Jedi disciplines. It is believed that he has mastered nearly all the known powers, previously unknown powers, and devises new ones at his pleasure.
- Source: Dark Empire Sourcebook
Essence Transfer:
If Palpatine were to fall in combat, he can use essence transfer to transfer himself into Superman, taking him over.
Palpatine claims he can take
anyone over.
Sidious has used Essence Transfer several times and can use it everytime he falls, making him pretty much immortal. It took the souls of every Jedi that had ever lived to finally take him down for good.
Telepathy:
There seems to be a misconception that this ability only works on the weak minded, though this is false. Palpatine has used this ability on people with great will power, such as Vader and Luke Skywalker. Vader himself was able to "will himself back to life" on one occasion.
Boarding his shuttle, he ordered the pilot to lift off. A pity, my son, he thought. You could have joined me and together...we could have destroyed the Emperor and ruled the galaxy in his place. As he stared at the severed appendage in his hands, a sudden flash of insight struck the Dark Lord, realization dawning like the sunrise of Bespin. Perhaps, if you will not be turned, little Jedi, a suitable substitute may be arranged.
Suddenly, Vader was struck to his knees by the horribly powerful voice that rolled like fiery thunder through his brain. The pilots struggled vainly to ignore the Dark Lord's...discomfort. "Yes, my servant," the voice boomed in his mind, dripping raw evil. "Come to Mount Tantiss, immediately. I shall meet you there, and we will discuss my new trophy."
"Yes...my Master," Vader gasped, feeling an icy stab of dread in his soul, as the Emperor's mocking chuckle still echoed in his mind. His Master had detected his rebellious thoughts. This discussion would be most unpleasant. Most unpleasant indeed.
- Source: The Thrawn Trilogy Sourcebook: Clone B-2332-54
Palpatine has used telepathy on Luke to compel him to the darkside.
Palpatine has used telepathy from across the galaxy, being able to project an image of himself to Mara Jade.
I think Telepathy is one of the main reasons for why Palpatine wins. Superman has been susceptible to mind control before and considering Palpatine's power, I think it's safe to say it'll be effective.
A perfect example being when Superman lashed out on Wonder Woman, thinking she was Doomsday due to mind control.
Force Drain:
Palpatine was able to slowly drain the entire population of the planet Byss, which had nearly 20 billion people.
Years ago, Emperor Palpatine chose Byss as his private retreat, and Imperial architects and engineers were commissioned to build him an opulent palace. Several million humans were allowed to emigrate to the world, where the Emperor and his adepts used the dark side to feed off their life energies. The planet's population eventually reached almost 20 billion, and all outgoing communications were censored by security agents.
- Source: The Complete Star Wars Encyclopedia
Imperial ships ferried millions of immigrants to the planet Byss, where the Emperor fed off their life energies through the dark side.
- Source: The New Essential Guide to Characters
"The galaxy is choked with beings. Billions die every instant. It is better to make use of this resource. At my retreat on Byss, the life force of its colonists supplied an energy pool to sustain my dark side experiments."
- Source: Book of Sith: Secrets from the Dark Side
Lightning:
It could be debated on whether lightning would effect Superman, though I myself am not sure, however I'll leave this here.
Force Storm:
Force Storm is an ability where a Force user tears the fabric of space and time, forming a Wormhole which possesses tremendous destructive ability.
This is perhaps the single most destructive Force power known. This power allows the Jedi to twist the space-time continuum to create vast storms of force. The power also allows limited control of these storms. Capable of creating annihilating vortices, the storms can swallow whole fleets of spaceships or tear the surfaces off worlds.
- Source: Dark Empire Sourcebook
Palpatine once summoned a Force Storm which ravaged Coruscant and transported Luke Skywalker to Byss.
He's capable of summoning more than one at a time.
The energy storm that took Commander Skywalker, this is not an isolated event. Similar Storms have been detected in several systems.
- Source: Dark Empire Audio Drama
Palpatine summoned a much stronger Force Storm to destroy the moon Da Soocha V, also destroying the Republic base and a whole fleet.
Precognition:
Precognition allows Palpatine to sense events that are going to happen. This ability has proven useful to him several times.
This should allow him to foresee the event with Superman.
Speed:
Superman's travel speed is greater than Palpatine's, no doubt, however there's a difference between travel speed and combat speed.
It's common knowledge that Superman is faster than Wonder Woman, however in combat speed it's different.
I believe Palpatine has the combat speed needed to compete with Superman.
In the Revenge of the Sith novel, Palpatine moves faster than Anakin could see.
Anakin blinked and rubbed his eyes again. Maybe he was still a bit flash-blind—the Korun Master seemed to be fading in and out of existence, half swallowed by a thickening black haze in which danced a meter-long bar of sunfire. Mace pressed back the darkness with a relentless straight-ahead march; his own blade, that distinctive amethyst blaze that had been the final sight of so many evil beings across the galaxy, made a haze of its own: an oblate sphere of purple fire within which there seemed to be dozens of swords slashing in all directions at once.
The shadow he fought, that blur of speed—could that be Palpatine?
Their blades flared and flashed, crashing together with bursts of fire, weaving nets of killing energy in exchanges so fast that Anakin could not truly see them—but he could feel them in the Force. The Force itself roiled and burst and crashed around them, boiling with power and lightspeed ricochets of lethal intent. And it was darkening.
- Source: Revenge of the Sith
This is impressive, because Anakin has reacted to a respectable fraction of lightspeed.
Obi-Wan was already making that exact move as Anakin spoke. But they were inverted to each other: breaking right shot him one way while Anakin whipped the other. The tri-fighters' cannons ripped space between them, tracking faster than their starfighters could slip.
His onboard threat display chimed a warning: two of the droids had remote sensor locks on him. The others must have lit up his partner. "Anakin! Slip-jaws!"
"My thought exactly."
They blew past the tri-fighters, looping in evasive spirals. The droid ships wrenched themselves into pursuit maneuvers that would have killed any living pilot.
The slip-jaws maneuver was named for the scissorlike mandibles of the Kashyyyk slash-spider. Droids closing rapidly on their tails, cannonfire stitching space on all sides, the two Jedi pulled their ships through perfectly mirrored rolls that sent them streaking head-on for each other from opposite ends of a vast Republic cruiser.
For merely human pilots, this would be suicide. By the time you can see your partner's starfighter streaking toward you at a respectable fraction of lightspeed, it's already too late for your merely human reflexes to react.
But these particular pilots were far from merely human.
The Force nudged hands on control yokes and the Jedi starfighters twisted and flashed past each other belly-to-belly, close enough to scorch each other's paint. Tri-fighters were the Trade Federation's latest space-superiority droid. But even the electronic reflexes of the tri-fighters' droid brains were too slow for this: one of his pursuers met one of Anakin's head-on. Both vanished in a blossom of flame.
- Source: Revenge of the Sith
Conclusion:
I believe Palpatine's use of Precognition and Telepathy are his real trump cards and considering Palpatine's willpower and the fact that Palpatine has influenced strong minded foes, I think it's safe to say he can influence Superman. I believe Palpatine will sense Superman and if he wants to, destroy Superman with telepathy across the galaxy, or even in front of him. Telepathy isn't the only way for Palpatine to destroy Superman, he has drain, force storms and essence transfer. Palpatine just has too many ways to win, but let's say Superman manages to defeat Palpatine. Palpatine then uses essence transfer to take over superman, then we have the most powerful dark sider in a Kryptonians body.
Winner: Emperor Palpatine.
