This video goes into depth on whether or not Darth Vader was stronger than Emperor Palpatine .... read more
Vader certainly had the potential to be the most powerful Jedi/Sith ever known - Sidious himself comments on this just before battling Yoda by saying “Darth Vader will become more powerful than either of us” - but his defeat on Mustafar by Obi-Wan literally severed that potential. read more
Darth Sidious is more powerful than Darth Vader in the Dark Side of the force, he can hide things from Vader and was only killed by Anakin Skywalker, feeling the good side of the Force. read more