This fight has been getting heated on Youtube lately
I don't know enough about Akuma to make a solid judgement. From my view, I think this is a difficult fight to call. On paper, I think Shao Kahn wins because of his feats, age, and him being an ex-god, but being a successful conqueror doesn't make you the best fighter in the ring. Also he really comes off as arrogant and sometimes incompetent.
Akuma on the other hand is focused, powerful, and extremely deadly.