Considering how Revan trained under a Tulak Horde holocron, and to my knowledge excelled at it, I would say that Revan would be the victor in any lightsaber duel. However. A Force fight would be a while. Sidious is a master of 'surprise attacks', as he is infamously known for. But Revan would be a hard person to surprise, short of having a battleship aimed at his back. . . Anyways. Revan hasn't done anything exceptional that we are aware of in terms of Force powers, save for a quote made by Darth Traya which is dubious at best.
We lack specifics to judge him on Force powers. If we go by his abilities in-game, well, the Force fight will be rather easy. Revan is equipped with all of the Dark Side powers, including a Force Storm. Yet it cannot be denied that his Force Storm is rather pathetic when compared to the one Sidious summoned, so from in-game experiences, he is no match for Sidious in the Force.
If Revan is quick, he can strike Sidious down after a 3-5 minute duel. Sidious is a master of defense and offense in DE, and when should Revan take the offensive, he'll be able to counter his moves for a little while before being struck down.
In a contest of the Force, I'm very confident Sidious would beat him.
Well, although we cannot be sure, it can be deducted that Revan is more of a defensive duelist himself.Now, this is only a theory, but in my mind, a valid one.
Jedi usually use a saber form that best suits their uses, but also one that goes hand in hand with their personal nature. Anakin uses Shien, an aggressive form. It mirrors his inner self. Obi-Wan uses a defensive form, Soresu. He is a 'classic' Jedi, so he chooses the least violence-centric form he can find. Makashi is a form based on dueling, and is filled with elegant and classy manuevers. It is a style reminiscent of the old ways, when gallantry and elegance were respected above all. And so it was chosen by Count Dooku.
As you can see, Jedi choose their styles based on what suits them, their character, more than anything. Now, there were those thousands who used Niman; they weren't the 'greats' of their time by any means. But they used Niman because it suited their purposes, their needs.
So, judging by Revan's cold, calculating nature, the way we waits for his opponent to reveal himself, and then strikes with Hell's fury, I'd say he uses a blend of a few forms. The ones that first come to mind are Soresu and Makashi. A solid defense to ward away any attacks, and a dangerously precise counter-attack for when he finds those openings. Seems reasonable enough. But it's just a theory people.