In my opinion it goes to Gray Fox. I Think he's stronger, faster, and cooler than MC. Master Chief is wielding any 2 weapons a replier may wish, and Gray fox has his suit and sword.
Gray Fox is the metal Gear Solid Guy. He's the one that can hold up the Leg of Metal Gear Rex, Which we'll assume is a lot heavier than anything MC has even consider flipping, and we'll give MC all the Grenades and specials he wants. Gray Fox is also incredibly resistant to anything but unarmed attacks.
What? You expect him to one-shot Master Chief? He will come out, sooner or later.
In that case, switch the beam rifle for Gravity Hammer.
Is Gray Fox fast as the wind and as agile as.. for example Karai? Because seriously, he needs to be VERY quick in order for Master Chief to not keep up.
The Grav hammer is the single slowest thing in existence. If Gray Fox couldn't dodge it, than I'd prolly start cutting... OMG you sig says Beeci... I'm so confused... even more now.
Also, Master Chief has quite the radar. He most likely would sense Snake before the moment of impact.
I guess you did not see the scene where Tatauros (S?) pulled Guility Sparks to himself. With the help of the hammer, Master Chief could drain Gray Fox's sword. The hammer is not slow, either. Gameplay possibly, but that is for game balance. Master Chief can lift tons, so out-of-game Master Chief would swing it like a bat.
I know it does I have wanted to change it, but got lazy
What we do know of the Energy Sword, is that it penetrates the shield, armor and instantly kills the spartan that has fallen miles from the sky and made meteoric impact to the ground without a scratch. The very same spartan that was hit by a falling warthog and did not even become pummeled or hurt.
Master Chief still has set abilities, strengths and feats trough canon. If we went with game mechanics alone, Archimonde would be the undefeated champion of KMC.