I will break old taboos here.
At this point, Sidious's only chance of victory is with sabers.
Sabers: Sidious (possibly)
Revan is no slouch when it comes to martial abilities; thanks to his amazing precognitive abilities, he is capable of making precise judgements and perform precise strikes. The manner in which he outdueled an Imperial Guard individual is indication enough.
As per Drew; Revan is skilled in all forms of lightsaber combat. However, Revan have no specific preference in case of Forms; he mixes his style if he feels appropriate.
Sidious have demonstrated the ability to blitz competent duelists. Though he have his share of losses in this aspect as well. His performance against the brothers indicate that he may handle Revan in this aspect.
Force: Revan
Revan's command of the Force is incredible and has received some serious hype.
Hype 1: Jedi Order's most powerful champion
Hype 2: Mighty Sith
Hype 3: Champion of the dark side
Hype 4: Command of the Force greater then that of any individual whom Meetra have met
Hype 5: Like Vitiate, understands the Force in ways that Scourge wouldn't ever perhaps
Combat performance wise;
1. Instrumental in defeat of the Sith forces in the Battle of Rakata Prime (destroyed Sith forces stationed inside Star Forge specially)
1. Defeated Darth Malak aboard Star Forge
2. WTFpwned Darth Nyriss
3. Came close to assassinating Darth Vitiate (As per SWTORE)
This is some serious shit.
At this point, Sidious is no where close to Vitiate in power. He cannot do much to Revan with his powers. In fact, I wouldn't be surprised if Revan flawlessely bends Sidious's FL back at him to give him the taste of his own medicine and injure or exhaust him in this manner.
As per Drew; Revan is capable of performing insane feats. However, Revan is very calculative in his choices. He doesn't steps out of boundaries unless pushed enough.
In the TOR game, Revan appears to be very impressive with the Force; his Force based attacks are unblockable.
All Out: Inconclusive
It took an Imperial strike team (comprised of some bad@sses) to defeat Revan aboard Foundary. And this is after 300 years of torture he endured.
Heck, it isn't even clear if Revan fell in this battle; existing rumors suggest that he used special powers to escape from the region (possibly bended time and space to perform this feat). If Revan is alive after this assault, it is possible for him to cheat death like situations.
In good shape, Revan is an overwhelming opponent.
I put the all out at inconclusive because;
1. Sidious may win with sabers
2. Revan may prevent Sidious from killing him by using his special abilities to escape
3. Sidious may get injured
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Haters gonna hate!