Stronger - Dark Side
Better - Light Side
I definitely prefer the light side, simply because though the dark side grants you power, it will ultimately destroy you. You're aggresiveness, anger, overconfidence and greed will doubtlessly get the better of you, and once you're dead, you're dead, you cannot achieve eternal life. The light side may not be as powerful but you are able to achieve immortality (eternal life)
The light side is like jogging, you may not be moving that fast, but it's everlasting, while the dark side resembles sprinting, you move a lot faster, but it'll be a matter of seconds before you run out of breath and collapse. In the olympics, Sprinters can run for like ten seconds (100-200m) before they tire out, gasping for breath, but marathon runners can run for three to four hours (40km) no problem.
Strength-wise? As always, it depends. The Dark Side would clearly be stronger if it didn't force you to become straight-up evil. Just using it corrupts you. Immediately speaking, it's just plain stronger. We know that Force users seem to exhibit an increase in Force potency almost immediately after embracing it, and combat-wise, it gives more options. But isn't the whole Force ghost think a Light Side deal? Or is that universal? Because supposedly being able to retain consciousness after death is supposed to be true power if we're to believe Yoda and Obi-Wan.
Preference-wise? Wouldn't anyone say Light Side? I don't think anyone wants to be part of oblivion when they die.
Light side is obviously more able to return, but that doesn't mean Dark Side characters can't do it. Exar did it, Marka Ragnos did it, Ajunta Pall did it. The strongest dark side people can do that too...
Also about the dark side corrupting you and killing you? Yes in a way it does, but for other reasons then just doing it. It has more to do with superiority over everything. That you are the strongest and the strongest should lead. Its about taking power and making yourself stronger, eventually that means you will die as soon as somebody stands up that is stronger.
The light side is more about harmony allowing you to last longer and probably learn more but in raw power it can not stand up against the Dark Side. Unless you are really skilled, the dark side will have more problems then.
This is not even necessarily because of the Light and Dark Side, because you can not honestly say a Light Side follower has no chance against a Dark Side follower it has more to do with the philosophy from Jedi and Sith. Those religious cults that preach the Dark and Light side. Personally i think that as long as you follow neither you can achieve real power. Neither light nor dark knowledge from both. Whether you use more dark or light side powers hardly matters then.
And on which i prefer? The Dark Side... Killing people is cool, at least in games and movies it is, besides I'm a sucker for bad endings