Space Marine hands down.
The tech used by the Spartans in Halo is not much more advanced then what our own troops have now. A Spartan, while enhanced, is not much larger then a normal marine. Finally their shield, while still a great feature, can still be brought down by normal rounds from an assault rifle.
A Space Marine is more then human, he is like another species unto himself. He is much large, stronger, and faster then any human could ever attain. His armor is composed of thick adamantite plates. He uses .70 caliber weapons with depleted radioactive shells for a normal weapon. Finally there is nothing that physically prevents a space marine from using the weapons of his enemy, they have decided not to. The Deathwatch uses xeno weapons as their needs demand it.
Master Chef would get beat to hell by any space marine, hell I doubt he could even beat a scout.