Assad is the more long-term evil, he could actually survive all this, while the IS is doomed to be destroyed. And Assad has killed much more people.
Yes, I'd rather take out Assad, and have the IS make some gains in Syria before they're taken out.
Is Bashar al-Assad a threat to the US? No. Is Bashar al-Assad a threat to Syria? Of course.
But it's not our job to look out for the best interests of the Syrian people. We're not a human rights brigade.
Indy, Starwatcher, you are neglecting or underestimating the consequences of an ISIS takeover on the Syrian people. The Shias, Christian and moderate Sunni communities would suffer just as they have in Iraq. ISIS would cleanse them of their supposed sins. They could make Assad's barrel bombs seem tame.