Well who would win?
A Spartan II
[url]http://deadliestfictionalwarrior.wikispaces.com/file/view/masterchief.jpg/196082332/masterchief.jpg[/url]
Or a Space marine of the Ultramarines chapter?
[url]http://images4.wikia.nocookie.net/__cb20130626181641/warhammer40k/images/1/13/Ultramarines_Artificer_Armour2.jpg[/url]
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A spartan would get rekt by an ultramarine. These BAMFs are the ones that laid the foundation for characters like the master chief to exist at all. Better armor, weapons, physical strength, speed, and reaction times are all possessed by the ultramarine. Combine that with absolutely no mercy or morales for those who go against the emperor of the imperium of man, you've got a huge problem on your hands.