We know when we are following our vocation when our soul is set free from preoccupation with itself and is able to seek God and even to find Him, even though it may not appear to find Him. Gratitude and confidence and freedom from ourselves: these are signs that we have found our vocation and are living up to it even though everything else may have seem to have gone wrong. They give us peace in any suffering. They teach us to laugh at despair. And we may have to.
~Thomas Merton No Man Is an Island

For being rulers of the universe, Palpatine and Darth Vader don't seem very happy. They look pleased, maybe, but neither appear to be completely comfortable even while possessing unlimited power. Granted, most of their fears result from knowing the treacherous nature of the Sith and expecting the worst, but that reflects the uneasiness that is central to the life of a Sith. We give Palpatine credit for his analytical prowess, but it isn't often that we think about the cost. Because he plans every minute detail of his career and that of everyone else involved, he loses his freedom. Although he is Emperor and often gets his way, he never gets to enjoy the freedom he has gained for himself.

"I'm afraid I don't believe in the will of the Force," Palpatine said, his smile turning apologetic. "I believe it is our will that matters. I believe that everything good in our civilization has come about not by the blind action of some mystical field of energy, but by the focused will of people."
~Matthew Stover, Revenge of the Sith

There is some truth in this statement. People do have the freedom to do good or evil, but there is an added dimension. Whether or not someone believes in the will of the Force, there still remains the question of how free we allow ourselves to be. If we analyze everything in our own lives and in our circle of friends and enemies, are we free? If we obsess about plotting and planning, worrying and fretting, can we be free? Not in my experience. And not in the Star Wars saga either. Yoda is an example of how someone does attain true freedom.

"Wars not make one great."
From my point of view, this is an illustration of Yoda's gratitude for being free from pride. He is free from being consumed by delusions of grandeur, free from the urge to be respected beyond worth. He is a humble servant of the Force and, as such, is free. It might later appear that he boasts of his vast knowledge and experience, but Luke himself nods in agreement that he isn't where he should be and that he needs Yoda's help. I believe Yoda demanded due respect with that comment, not worship.

"For my ally is the Force, and a powerful ally it is."
This, too, could appear to be a prideful remark, but again I disagree. Yoda is expressing his complete confidence in the Force. He makes no effort to mislead Luke that he himself is the powerful one. The Force is the source of his strength, and he considers it a gift even to commune with it. And he doesn't expect honor or wealth or even good health as a reward for giving himself to the Force. He wants only to be united with the Force, and he gets that even in death. By being a slave to something good, by doing what he knows is right, and by leaving all consequences to the Force, he is free. While not above worrying about how things turn out, Yoda never loses his freedom and inner peace. He finds true freedom even while driven from power in the bright center of the universe, and while living in a snake infested swamp. In any suffering, Yoda still has freedom.

But not the Sith. Their days are full of plotting treachery, fearing treachery, demanding worship, and threatening subordinates. They are not at all free, though they work harder for it than the Jedi.