A free and democratic Syria can not be built within the next several generations. The best we can hope for is the least malignant government possible (in terms of the threat they pose to outsiders), and that is most likely Assad.
Turkey is the remaining Terrorist source in Northern Syrian. There will never be freedom in Syria as long as Turkey is ruled by Erdogan the Islamist. And if he were absent, I doubt that Turkey will change their ways. They have not since the beginning of the Ottoman Empire. There are large pockets of Syrian citizens who have demonstrated over the past 5 years that they can live together peacefully; Kurd, Ezidi, Alevi, Arab and Assyrian. Except for the small pocket left along the Iraq border East of the Euphrates which is encircled, ISIS in Syria is gone. Assad may be the best that can be done in the short run because of the neighbors, but the people who fought and defeated ISIS (with U.S. help) deserve a chance to live in freedom.