I think the evidence mounts that it was the rebels. The Russians seem to have supplied them with the kind of launchers they needed. They were firing them at planes. They were proudly claiming successful hits on helicopters, transport planes, fighters. And this plane. Until they discovered it was a civilian aircraft.
The fact they haven't admitted it and used the obvious excuse of accidents of war tells me that there's an effort to preserve Putin's narrative. But I doubt he's going to succeed in persuading many folks that he didn't supply the rocket launchers to the rebels and they didn't use them.
http://press.ihs.com/press-release/aerospace-defense-terrorism/ihs-janes-analysis-capabilities-ukraines-missile-systems
http://www.bbc.com/news/world-europe-28378388