The [url=http://.wikipedia.org/wiki/Kardashev_scale]Kardashev Scale[/url] would be a good somewhat-empirical way to decide this. Forerunners have already achieve a Tier III civilization, and Precursors may have reached even higher. While some technology in Star Wars would appear to be Tier III (in particular their traveling capabilities), most of the civilizations seem to be in a Tier II category. This is likely due to the original creators of the series not comprehending how much energy a galaxy-wide civilization would be able to control. I'd say, from what we've seen, it goes to Halo.