For me the most powerful force user is Galen Marek, aka Starkiller from the Force Unleashed series. I know it's not canon anymore, but for me all the games EU is still canon. That guy is probably the most powerful force user ever, he stopped a goddamn star destroyer using the force.

Thank you for the reply. Regards.

I'm wondering if you can turn to a sith warrior and learn their skills as a jedi sentinel? Does the light/dark bar on the character screen actually affect the storyline?