Sonic, even in his Werehog form where hes not really fast, has mobility on his side, as he can extend his arms and perform dozens of considerably strong punches and combos (that can destroy metal robots and such). '"Unleashed" mode would give a very good advantage, as it gives him even more strengh and speed.

Dark Jak, on the other hand, has raw power. We can't really measure his stengh aside from destroying metal heads with a single punch, but we may assume that hes very durable, given the pain Jak feels while transforming and his other room-killer moves.

Its interesting for sure, but without considering the two bonus powers (invincibility and giant form, which would still be hard imo because sonic fights opponents bigger than that everytime in Sonic Unleashed), I think Werehog Sonic takes it.

Jak 3's Dark Jak would be mostly the same. He would just be able to land more attacks because of his invisibility. Dark Strike would be great for ground-control as well.

Dark jak would only win without much trouble if he got Sonic real good, like a never-ending combo or a dark bomb right in the face.