You are all wrong. It is Darth Bane who IS the most powerful Sith lord to ever live. He is the one who reverted back to the old Sith teachings which was the rule of two which Palpatine still followed!
But Palpatine is a cowardly Sith lord. He knew Vader had much potential and was very powerful and hungry, but Palpatine was so much more wise then Anakin at the time, he knew Anakin would not win against Obi-Wan. So after losing to Obi-Wan in that epic fight, he saved Anakin to have power at his side. The suit that he put on Vader was meant to keep him at a disadvantage so Palpatine would never have to worry about losing his power from Vader.
Darth Bane actually wanted his Sith apprentice to become more powerful and learn more so the Sith would stay strong and he knew the fastest way to do this was the rule of two. This is where Palpatine let the power consume him, and he lost control of the darkside and was not able to harness it, it made him stupid.
In my mind, Palpatine crippled the power of the Sith. Bane was able to control the power of the dark side better than any other Sith lord, which by definition would make him the most powerful Sith lord. He was so powerful, he was able to withstand the thought bomb.
He learned to use the orbalisks to make him even stronger with the darkside of the force, but they were halving his life because of all the darkside energy that was pulsing through him so he had to get rid of them. Not to mention all the teachings he learned through his journeys from some of the most powerful Sith lords to ever live (forget who, I know Andeddu is one and others along with old scriptures and all the books he read).
Darth Bane had lost to his apprentice, but only to continue on living through her when he performed the ritual that gave him the ability to live on in another being. (I forget what it's called) Palpatine has crippled the power of the Sith and they would be a lot stronger if he would have done right by Vader and taught him like he was supposed to instead of holding many secrets from him. Vader never even came close to his potential and Vader would have ended up being the most powerful, but with a poor teacher and nobody to help you reach that potential, how can you?
Which brings me back to Bane. He pretty much lost his self within the darkside of the force and became a part of it. He committed the rest of his life to learning the teachings of the Sith and has acquired more knowledge than any other Sith lord who has ever lived.