Dueling Abilities:
Darth Malgus
Darth Malgus was one of the greatest warriors of the Old Republic. Even Sidious praised his skill on the battlefield.
Malgus has defeated notable Jedi such as Jedi Knight Satele Shan, Jedi Master Ven Zallow, Jedi Battlemaster Kao Cen Darach and Aryn Leneer.
Malgus's duel with Ven Zallow
https://www.youtube.com/watch?v=wOLANti8UCY
Malgus's duel with Satele Shan
https://www.youtube.com/watch?v=z0RuR3FREFw
Malgus's duel with Kao Cen Darach
https://www.youtube.com/watch?v=mm4JEZudf0c
Malgus's duel with Aryn Leneer
She did not wait for Malgus. She bounded across the hangar, her speed augmented by the Force, the lines of her blades leaving a blur of light in their wake. Malgus held his ground, blade ready.Malgus was said to have been one of the greatest warriors of his day.
She stabbed low with her primary blade, high with her secondary. Malgus leapt over both, flipped, landed behind her, and crosscut for her neck.
She ducked under it while spinning into a reverse leg sweep that caught his feet and tripped him. When he hit the ground, she rose, turned, raised both blades, and drove them down in a parallel overhand slash. Malgus somersaulted backward, and Aryn’s blades cut gashes in the floor of the hangar. Sparks flew.
Malgus bounced up from the somersault and loosed a telekinetic blast that lifted Aryn from her feet and blew her across the hangar. She slammed into one of the shuttle’s bulkheads, but used the Force to cushion the blow so that it did no harm. Bouncing off the cool metal, she charged Malgus. As she ran, she cast first her own lightsaber at Malgus, then Master Zallow’s, using the Force to guide both.
The attack caught Malgus unprepared, and Aryn’s blade bit into his armor. Sparks flew and Malgus winced, snarled with pain. He ducked under Master Zallow’s blade, and Aryn recalled both to her hands as she ran. The moment she had them, she cast them both at Malgus again.
But this time he was ready. Augmenting his speed with the Force, he flipped high into the air and out of the way of both. She anticipated his movement, however, bounded forward to cut him off and landed a flying kick in his chest. He used the Force to diminish the blow’s impact but it drove him back a step and she heard his breath hitch through the sound of his respirator.
He recovered, roared, raised his blade high to cut her in two, and brought it down. But she had already summoned her own blade back to her hand and interposed it in a parry.
Malgus’s strength drove her to her knees. She held out her other hand and pulled Master Zallow’s blade to her hand, stabbed for his stomach with it.
Malgus sidestepped the stab, though it skinned his armor and showered sparks. He pushed her blade to the side with his own and kicked her in the face. The strength behind the blow blew through her defenses, caused her to see stars, loosed teeth, and sent her head over heels backward. She landed on her knees, stunned, seeing double.
She rose, swayed on her feet, seeing four blades in her hands rather than two. Something was in her mouth and she spat it out—a tooth, the root forked and bloody.
“You are a child to hate,” Malgus said, his tone incongruously soft as he stalked toward her. “Your anger barely smolders. You are a fraction of what you could be.”
She needed time to recover her senses, some distance from Malgus. She backflipped high into the air and landed atop the Imperial shuttle. Her mind was beginning to clear.
“Your Master was also misguided. He thought to defeat me with calm, but failed. You thought to defeat me with anger, but carry too little, despite your loss.”
Aryn’s vision began to clear. She felt more herself.
“Be grateful for that, Jedi. Anger exacts its own price.”
Again she felt the odd sense of sympathy or pity adulterating the otherwise pure hate flowing from Malgus. His eyes went to Eleena, her body crumpled on the landing pad’s floor.
As Aryn prepared to leap at Malgus, he held forth a hand, almost casually, and lightning sizzled through the space between them. Aryn interposed her lightsabers, but the power in the lightning exceeded anything she had felt from Malgus before. It blasted through her defenses and both lightsabers flew from her hands. The lightning seized her, lifted her up, and threw her from the top of the shuttle.
As she flew toward the deck, she smelled burning flesh, heard screaming, realized that it was her flesh, her screams. She hit the ground hard and her head bounced off the ground. Sparks erupted in her brain, pain, and everything went dark.
-Source: Deceived
Even before the Great War, Malgus was widely regarded as one of the greatest warriors in the Sith Empire.Is it assumed that Malgus was killed by a Republic Foundry, however there has been evidence showing that he may have survived. This clip shows Malgus frozen in carbonite 5 years after his supposed death.
-Source: The Old Republic Encyclopedia
https://www.youtube.com/watch?v=aHqzDx2X9sc
Just thought that was interesting. Malgus likely trained in Djem-So, Soresu and Shien, as I think that was the typical forms in use for Warriors back then.
Luke Skywalker
Luke as of ROTJ was an equal match for Darth Vader, one of the best duelists in galatic.
The fight this time was far more balanced. Vader discovered that Luke was his match, and, once again, the Sith Lord found his thoughts straying to an alliance between them against the Emperor.
Luke had indeed grown powerful since Bespin, and he was an equal match for his father.
- Source: The Official Star Wars Fact File #111
By the time of the Battle of Endor, Luke Skywalker had studied some lightsaber technique from Obi-Wan’s journal and greatly advanced his abilities. Without a master, such advancement would have been impossible for most, but Skywalker’s unparalleled aptitude makes him a match for Darth Vader in their fateful duel onboard the second Death Star[…] and his lightsaber technique is so superb that he is able to duel the Dark Lord on even footing - and finally able to defeat a man who is a powerful living product of the ancient Jedi sword traditions from time immemorial. Such an achievement with little formal training is a testament to Skywalker’s innate abilities and instinctive skill.
- Source: Fightsaber

Luke way before his prime and without training contended with 2 magnaguards, droids who are capable of taking down Jedi Knights.

Luke was a Djem-So practitioner, one who matched his father and was a great duelist.
Malgus and Luke are similar in terms of pure skill, however I feel Luke gets the edge for his adaptability and potential. Malgus would not have been able to be considered an equal like Luke could.
Dueling abilities = Luke Skywalker
Force Abilities:
Luke Skywalker
He was capable of briefly holding a AT-ST in stasis and he has casually pushed Stormtroopers.


Darth Malgus
Darth Malgus was a very powerful darksider.
He's shattered columns with a force scream (involuntary force power)
Anger refilled him, overcame him. A shout of hate, raw and jagged, burst from his throat. Power went with it, shattering a nearby column and sending a rain of stone shards through the room.While injured, he's blasted several tons of duracrete and steel.
- Source: Deceived
Malgus stood in a pocket under a mountain of rubble, legs bent, the power from his upraised hands preventing several tons of duracrete and steel from crushing him. Dust made his already troubled breathing more difficult. He coughed as the words of his father echoed in his mind.He's also choked out Jedi
He'd been sloppy, so lost in his need for revenge that he'd failed to properly evaluate the Jedi's power. He'd surrendered his reason to bloodlust. But no more. With an effort of will, he contained his anger, controlled it, made it a whetstone against which he sharpened his power. Using the Force, he blew the rubble up and away from him. It fell with a crash into the adjacent buildings. A Force-augmented leap carried him out and over the heap. The Jedi's eyes widened as Malgus hit the street. Malgus sneered and charged.
- Source: The Third Lesson
Another Jedi stepped in front of him, blue blade held high. Malgus barely saw him. He simply extended a hand, pushed through the Jedi’s insufficient defenses, seized his throat with the Force, and choked him to death. Tossing the body aside, he moved toward Zallow.This round is pretty close, though I think Malgus gets a slight edge in force abilities.
- Source: Deceived
Force Abilities = Malgus
Physical Abilities:
Luke Skywalker
Luke's greatest physical feat is no doubt matching the strength of Darth Vader.
Although Darth Vader and Luke Skywalker are equally strong in the Force, their duels are more than just about physical strength.
- Source: Beware the Sith
Luke drove Vader back to the stairway that descended to the turbolifts, then kicked out with his left leg, knocking Vader from the upper platform. Vader groaned as he flipped over backward and landed on the metal floor below.Darth Malgus
- Source: Return of the Jedi Junior Novelization
Malgus on the other hand has survived being buried under a mountain of rubble and he killed two Jedi after.
I'd personally give Luke the overall edge. While Malgus is a beast, he doesn't match the strength of Vader.
Physical Abilities = Luke Skywalker
Conclusion:
While Malgus could win via force abuse, the most he usually ever does in his duels are simple force pushes and shoves. Even though he is capable of more, this seems to be his preferred abilities. These are not things that Luke can't deal with. In the end, Luke would win due to his superior bladework.
Winner = Luke Skywalker