From what i've seen, played, watched and listened to about both of these guys I think Revan would win in the end.
Galen has incredible potential but even in his prime he didn't seem to have complete control of his full power. He did have expert control over his more basic force powers however most of the time he was limited to lifting a few people at a time, some lightning and most to his credit a powerful shockwave. With that said when pushed to his limits his force powers might equal Revan's own, most profoundly indicated when he was able to pull a Star Destroyer out of the sky while defending himself against the turbolasers of said Star Destroyer and several Tie fighters.
Galen was also skilled in all 7 basic forms of lightsaber combat, this not only gave him a large variety of techniques but also the ability to quickly recognise his opponent's style and counter it. That combined with his diciplined force abilities which he commonly incorporated into his lightsaber combat eg. electrifying his saber for extra damage led to him defeating Vader and then immediately afterwards the Emperor aswell.
Galen's biggest weakness was his instability. Years of torment at the hands of Vader combined with his visions of his past and regret over his actions as Vader's apprentice left his mind susceptible to taunting and aggression. That's why he very nearly ended up turning to the dark side and killing Vader.
Revan seems to be an overall more effective warrior. Where Galen has brute power and a decent amount of tactical skill, Revan was a general in the Mandolorian Wars as leader of the Revanchists giving him far more tactical training and experience. This means that in one on one combat he should be able to better control the duel.
His force abilities are some of the most powerful known in the Star Wars universe along with Galen's. He didn't pull any Star Destroyer from orbit however his attunement to both sides of the force meant he could effectively get the best of both worlds. He could conjure up force storms and hurl massive boulders with little to no effort which indicated that he had more control and more power than Galen at his basic level. When pushed to his limits Revan could force augment his abilities to match Galen's force augmented strength, speed and agility almost blow for blow and as i've said while Galen seems more of a brute force fighter in comparison Revan is much more precise.
Revan's Lightsaber skill was also extremely formidable. His greatest strength in saber combat was he precognition ability which allowed him to respond to attacks before they happened. That would make it extremely difficult for Galen to land any attacks even with his force infused combat style and give Revan opportunities to counter more often than Galen.
Revan's biggest triumph would most likely be his final encounter with the Sith Emperor. For those of you who aren't familiar the Sith Emperor i'm refering to went by the name of Lord Vitiate. Vitate had quite literally sucked the power and life of an entire planet dry in order to make himself unimaginably powerful and close to immortal, Emperor Palpatine would not even be close to matching Vitate in any way. There is no way of knowing whether Revan would have won the fight due to how the book ended and while what we did see was the Emperor overpowering Revan i feel that in the end Revan would have defeated him. The point i'm making is that Galen managed to defeat Vader and the Emperor but Galen was then killed by the Emperor when he let his guard down, when both Palpatine and Vader would have been cast aside by Vitate albeit not immediately. What that tells you is Revan can achieve more than Galen, not necessarily because he's more powerful but because he is more effective.
It comes down to the style clash of Revan against Galen. As much as i love Galen i have to say that he is little more than a hammer, an extremely powerful and effective weapon but that's all he is. Revan is more precise, more diciplined and can can just about match Galen in terms of power. But with his keen tactical mind and pre-cog abilities Revan can outclass Galen and come out victorious.
That's just my opinion, i'm no expert on these guys but am in no way biased to one over the other. I love both Revan and Galen, they are two of my favourite characters.
Quotes from TFU and Starkiller's philosophy, understanding and skill:
Even as he mulled over this new development, a familiar snap-hiss sounded to his right and a glowing blue-white blade sprang to life in a dark corner of the hangar.
Instantly in a fighting crouch, the apprentice brought his own blade up to block the blow, teeth bared in a delighted snarl.
He and his adversary held the pose for a bare second, lightsabers locked across their chests. The apprentice quickly sized up the being who had attacked him. Human male, fair-haired and bearded, with calm, serious eyes and a firm set to his jaw. Anyone within the living memory of the Clone Wars--or possessing free access to the Jedi Archives--would have recognized him completely.
Jedi Master Obi-Wan Kenobi, High General of the Republic and master of the Soresu form of deadly lightsaber combat, slid his deadly blade down to the right, ducking at the same time to avoid the inevitable countersweep. Sparks flew as the apprentice Force-leapt high into the air and landed with perfect agility on top of a stack of crates. He reached out with the Force with his cupped left hand and swept a metal tool kit across the hangar bay, toward his opponent's head. Kenobi ducked and leapt up after him, deflecting a flurry of blows that would have left an ordinary man in piece, then responding with a sweep of his own that sent the apprentice dodging backward, jumping from one stack to another in temporary retreat.
So the duel proceeded for almost a minute, with Kenobi and the apprentice dancing like acrobatic Gados from stack to stack, lightsabers spinning and clashing, racks and tools turned into temporary weapons as they hurled themselves from one to the other. The racket was enormous, and the threat very real. Kenobi slashed a new rip in the apprentice's combat suit with a move that would've taken his arm off at the elbow had he not moved in time. Twice he felt rather than saw the Jedi's blade sweep over his head.
The apprentice wasn't afraid of dying. His only fear was of failing his Master, and that fear he put to good use. The dark side rushed through him, made him strong and resilient. He felt more powerful than he ever had before.
Vader was sending him to hunt one of his old foes--and how better to warm up for a mission than killing the man who had once been the most famous Jedi in the galaxy.
Alive with murderous intent, the apprentice rushed forward, his red blade swinging, to finish the job.
Originally posted by KylarWhite
You make a pretty big assumption, saying Vitiate could sweep away both Palpatine and Vader without too much trouble.