Saying Syrian rebels these days is about as Vague as saying some Major League Baseball team won the World Series. :-)
I’ve read this article and I’m still not sure which side they were on.
Apparently, the guys on the ground who killed the pilot were al Queda affiliated. They are the bulk of the “rebel” forces in Idlib. It is the largest military force that al Queda has yet fielded anywhere (~30,000)
They were likely the same ones who fired the Turkish-supplied missile that brought down the plane. It might have been Turkish military themselves though, as they operate in the area.