Although I wish it were otherwise, I feel the overwhelming odds are that MH17 was shot down by a Buk-M1 surface-to-air missile fired by the rebels (but supplied by the Russians):
1. The rebels, notably generalissimo Strelkov actually claimed to have shot down a government An-26 in the general area of the MH17’s demise. The social media claims in question have been retrospectively deleted, but in this age nothing is truly lost.