Kratos, high to very high diff - unless I get more feats about Oni - . Physically, Kratos is superior to Akuma in all stats (At least in base), and he's the complete opposite of a martial artist. If Akuma tries to beat him in submission, Kratos will likely brawl him to the ground, where he'll murder the demonic fighter.
Akuma got plenty of powers, I know, but most - if not all - of his chi based projectiles can be deflected by the Golden Fleece, and Kratos has hax on his side.
Shun Goku Satsu is a tough obstacle, however. If Akuma grabs Kratos to use that thing, Kratos is done for. However, Kratos can do the same thing with the Claws of Hades, and he can shield himself using the spartan squadron summon.