Well, you might be right, Its indeed true that Assad SEEMS to be a LESSER evil here(but an evil nevertheless. lol). Its not really because Assad is any better, its just that ISIS and other Islamic extremist/terrorists groups target virtually any country/power indiscriminately, Reason they have attracted so much media attention. Don't also forget Assad has tortured/killed thousands of his own people during his father's reign and his own reign a la monarchy. lol Plus Assad also supported these same terrorist/Islamist groups against U.S/British forces when we were trying to stabilize Iraq, he openly justified his support for these radical Islamic groups(Al Qaeda included) as Jihad against infidel invaders. lol The same slogan ISIS and other extremists group fighting his regime are now using against him today. call it Karma.
Dont forget that these groups Assad openly supported killed not just dozens/hundreds of American/British soldiers but also tens of thousands of Iraqi civilians.
This is something many people forget. lol
Iraq asked Syria's Assad to stop aiding 'jihadists': Former official | Middle East Eye
Syria's Financial Support for Jihad: Syrian Terrorism :: Middle East Quarterly
Has Damascus Stopped Supporting Terrorists? :: Middle East Quarterly
Its for this reason that i have no pity for Dictator Assad and his regime. But as you said for now, ISIS threatens our interests more than the butcher Assad, so guess its understandable we strike ISIS for now, and let Assad gain some ground. That's Geo politics anyway, sometimes have to dance/cooperate with the enemy for a while.