Darth Vader vs Darth tyranus

Vader stands a perfectly solid chance of winning despite what his lowballers insist. In fact, multiple sources say Vader eventually overtook his Revenge of the Sith iteration:

Many years later, Obi-Wan and Darth Vader duel a second time. The Sith Lord is now more experienced and powerful.

-- Beware The Sith

This duel was very different from their last. Obi-Wan was older and weaker while Vader was even stronger, fueled by hatred and thirst for revenge.

-- Jedi Battles

In his duel against Darth Vader on Bespin, Luke Skywalker reveals himself as an extraordinarily gifted artist with the blade who has largely taught himself. After a single brief session with Obi-Wan Kenobi years ago, and only a short time with Yoda, Skywalker is able to hold up against a Dark Lord of the Sith at the height of his powers.

--Insider 62

Ben was still clutching his lightsaber when he reached an access tunnel that led back to Docking Bay 327. As he entered the tunnel, he sighted a tall, shadowy form at the tunnel's other the end. Even if Ben had never seen Darth Vader's cybernetic incarnation via a HoloNet broadcast on Tatooine, he still would have sensed the power of his former apprentice, now concealed within black armor.

-- The Life And Legend Of Obi-Wan Kenobi

“This is a fight you cannot win, Darth. Your power has matured since I taught you, but I too have grown much since our parting. If my blade finds its mark, you will cease to exist. But if you cut me down, I will only become more powerful. Heed my words.”

-- A New Hope

His power was great, now, greater than it had ever been. It shimmered from within, and resonated with the waves of darkness that flowed from the Emperor.

-- Return Of The Jedi

You are Darth Vader, Lord of the Sith, master of the Dark Side of the Force. Once a power for good in the galaxy, you are now feared as the ultimate evil. Obi-Wan Kenobi, a Jedi Knight, opened you to the power of the Force. You became his apprentice and learned the ways of the Jedi. But Kenobi's methods were slow and difficult, not quick and easy as you hoped they would be. So you gave yourself over to the Dark Side, allowing it to consume you so that you could be reborn in a more powerful image. Now you stand with the Emperor, bent on subjugating the entire galaxy to his New Order.

-- Lightsaber Dueling Pack: Darth Vader

More powerful in the Force than ever before as well as a master of the lightsaber, Darth Vader prepares for his final battle as the Rebel fleet hammers the fully operational Death Star.

-- Darth Vader Return Of Anakin Skywalker