Biotic Shepard would just use Lift to send Master Chief into the stratosphere. Then Master Chief gets to experience what it feels like to be hit in the face with a planet.
He already did that and survived with essentially zero damage. Remember the opening of Halo 3?
I'd vote for the Master Chief. Out of his suit he's equal or superior to Shepard in strength, speed, and reaction time (remember, all the SPARTAN IIs were augmented to superhuman levels to allow them to survive using the MJOLNIR armor, and it's stated in
The Fall of Reach that their reflexes are literally too fast to clock; the same novel had the Chief beating several of the USMC's equivalent to paratroopers with his bare hands until at least one was dead and all of the others were in traction.....as a teenager), but he exclusively fights in power armor that increases his strength until he can literally punch through light armored plating and increases his speed and reflexes just as much. Plus the actual protective capability of the armor, which includes energy shields equal to or superior to Shepard's shielding.
Shepard may be a badass, but the Master Chief has taken on a fighter jet unarmed in the first novel and won. He literally slapped an incoming anti-tank missile out of the air. Shepard simply can't compete. Not unless he/she gets MJOLNIR armor.
