*cough*Sky Lynx*cough*
If we were talking IDW Sixshot I'd agree. It wouldn't even be a challenge. I mean, IDW Sixshot is literally a civilisation ending weapon all by himself. But G1 Sixshot was almost beaten by Ultra Magnus. And ol G1 Magnus wouldn't stand a chance against Prime Predaking. He did nearly kill Magnus and Wheeljack in TF:Prime (in one of the best fight scenes in TF animation), they were only saved by Optimus' intervention.
So I'll give this one to Predaking.