I honestly have very little interest in watching this show, but as a proud Star Wars nerd I will say that of Darth Sidious' apprentices, Darth Maul had the most potential to become a great Sith Master. Jedi just don't make good Sith. Its not something you become, its something you are born for.
I would agree. The whole Darth Vader thing is different from Darth Maul. As a Sith, Vader just could not cut it. He did not have the passion for the Sith Order; Vader was tricked into becoming a Sith. He did not embrace its ways like Sidious and Maul did.
Witness Maul's line in the Phantom Menace;
"At last we will reveal ourselves to the Jedi. At last we will have revenge!" This is someone who knows what he's talking about. he knows what side he's on, no hesitation or regrets here.
Its obvious he does not want revenge on the Jedi for stealing his candy when he was a baby; Maul wants revenge because of the oppression the Sith suffered under the Jedi; the complete repression of their beliefs and the extermination of their way of life.
When Maul fought, he fought for the Sith Order not for himself. Thousands of years of hatred, rage and suffering as his legacy and with the entire future of the Sith Order are at stake from Maul's point of view.
Now witness Vader's line when he becomes a Sith;
"What have I done, what have I done..." Yeah, i don't think he really gets it...
Vader only became a sith to learn a sith force technique to save his wife. When Vader fights its for some petty slight he feels has been done to his person (padme cheating on him with Obi-Wan).
Basically: Darth Maul spends his free time training, scheming how to kill Jed, and anyone else who gets in the way of the Sith, and plans for galactic domination and the entire destruction of an aeons old galactic ruling body (The Old Republic). Darth Vader spends his free time rolling on the grass with Padme. It does not take a genius to figure out who will win in a confrontation between the two.