Sending advisers to Iraq and Syria? Of the list of options, this may not be the best nor the worst, but probably will join the list of the mildly effective at best.
I am not so worried about Americans on the ground abetting ISIS's recruitment since I have yet to hear that ISIS has had a problem recruiting. On the other hand, if someone tells me that ISIS has had problems recruiting, then I would advise against anything that would help them.
Sending in Special Ops to advise the Kurds and other elements of the Syrian opposition might deter air strikes on them by the Turks and Russians (respectively). Which would be a good thing. On the other hand, it might not. And then what? That is the part that bothers me.