Unfortunately there seems to be no better option than keeping Assad in power. Certainly not ISIS. Nor the renamed Al Qaeda, both of whom are American allies in the fight against Assad, but absolutely not fit to govern.  And not the Kurds either, since Turkey will not accept that they take over as they would be a threat to them. 
So, if not Assad or these other groups, who is left? 
Looks like either a war without end, or Assad.