Fenix is, unfortunately, a non-factor in this fight, as the other combatants are all altered, either by genetics or technology. Radec will be a good comptetitor, but he really is the lesser version of John 117. The fight will come down to Master Chief and Captain Titus. But, the weaponry, armor and altered genetics are all in favor of Titus. He has 2 hearts, multiple sets of other vital organs (2 stomach, 3 sets of lungs, etc), glands to purify air and nuetralize poisons in the body, his entire nervous system is protected by a very dense bone growth that acts as a plating under the muscle tissue. MC probably has raw speed and agility over Titus, but barely if at all. Titus is far stronger and durable than MC, before and after armor is put on.
MC has his Mjolnir Mark IV Power Assault Armor, but that is very outclassed by an Astartes' Mark VIII Errant Power Armor. MC does have his versatility in armor modes, but that does nothing when you are fighting a guy whose armor is built from the same materials that space fleets are made of.
Space Marines just outclass any other type of soldier...for the most part, and defintely here.