First off, canon according to interviews is that there is a distinct dark and light side to the force, and that the dark side represents a corruption of the same - namely, because you're taking the living energy of the universe and bending it to your will.
Of course, a ton of different perspectives have been offered by different writers. Personally, I'm a fan of Zahn, who cleaves fairly close to the movies. Generally speaking, the Sith are more directly powerful. Because they are controlling and manipulating the energy, they can often gather it into single large uses - but it's a rare Sith who can manage things like battle meditation [which was also rare amongst the Jedi - but you'll note that unlike Joruus and the Emperor's dark hands, the Republic troops don't suffer under the guidance of their leaders]. The dark side, on a personal scale, offers a simple solution to problems, which makes it attractive and easy to grasp - have a problem? Throw the force at it!
The light side, on the other hand, requires a lot of restriction. To fully understand the light side requires a lot of willingness to serve the greater need, which often means neglecting personal gain. However, as a rule, that offers greater awareness - look at the Hand books, where Luke notes that because he's been using the Force so directly and centered it so much on himself, his 'fine-tuned' control and more passive understanding is limited. In this way, the value of the Jedi arts is in manipulation and understanding, and the role of intelligence in battle cannot be underestimated... and hey, if that fails, a lightsaber can do some serious damage.
Very interesting, but I have to disagree. The dark side represents corruption no more than putting a hydroelectric dam at a river makes you evil. Look at Revan: even when redeemed, once he remembered his past, he used the dark side without being corrupted. The dark side is only corrupting if a person lets it corrupt him. Windu, for example, used the dark side, but controlled it, albeit difficultly. The way I see it, the light side is hard to learn, and hard to master once learned. The dark side is easy to learn, but its great power corrupts all those but the truly great masters. When the dark side is corrupted by personal ambitions, it becomes weak, only a "have a problem? Throw the force at it" weapon. Those who do grasp the power of the Dark Side (Revan, Galen, and to a lesser extent Windu) Become the most powerful of all jedi or sith. in a way, they rise above them, becoming true Masters of the Force, because they are not held back by prejudices from either side regarding such trivial things as which side is stronger, as they know they complement eachother, and should both be used: the power of the dark with the restraint of the light to preserve both the greater good (light) and those they love (dark).
