Is the dark side stronger than the light side?

Well there might be an error in considering the Dark Side and Light side to be two separate things or sides. They both seem to be methods of manipulating the force.
Take force lightning for example. Jedi don't use it, but Yoda absorbs it during his fight with Dooku with ease. He says "Much to learn, you still have," as if he knew of its properties. And he must to be able to manipulate it so as to not cause him harm.

To my understanding, emotion is the catalyst of the force; negative emotion fueling the "dark side" and positive emotion fueling the "light." People fall more easily to the dark side because they can more easily feel anger than its foil.
How I see it, the difficulty in becoming a Jedi is developing yourself to the degree that positive emotion comes easier to you than negative emotion. Thus, it can become a stronger source of power. Sith train their negative emotion, though they too focus on self discipline. If you watch Darth Maul, he is calm and composed in every scene but the fight scenes.

So to answer your question, I think that the Light and Dark side of the force are equally as potent and only depend on the caster, though the Dark side comes easier than the Light.
The Jedi choose not to use it because it leads to corruption and death. Though I believe once you gain mastery over your emotions, you can swing to either side and be equally as powerful.

EDIT: The fight with Yoda and Darth Sidious was a stalemate in my eyes. The only reason Yoda lost was because he fell further than Sidious at the end, and the plot needed to be continued.
He was also 800 years older than Sidious. I think he was well past his prime.