i've got my SM codex right infront of me guys so if you need any info I'm here lol. Any way Im going to have to go with the SM. Some info about the initiation programme you need to go through to be a SM.
" Each battle brother of the Adeptus Astartes is a champion, a hero of a hundred campaigns. even before their transformation from man to superhuman they are the bravest and most promising scions of their worlds, most hailing from fierce warrior cultures on the deadliest death worlds. When a Chaper select a potential recruit for training they acceot a new son into their family, and it is fitting, therefore, that they take the greatest care in his selection. Each chapter selects recruits in its own way, be it by competition, scrutiny under adversity or the most sacred rituals."
"These Neophytes are subject to the most careful observation and rigorous testing before they can even begin their training. The Chapter Apothecaries examine their flesh down to the cellilar level to ensure that they are free of the taint of the mutaion and strong enough to survive the training."
" over a period of years, the neophyte receives each of the biological implants that will transform him beyond the pinnacle of human potential into a Space Marine battle brother"
" As a Neophyte receices the Chapters gene-seed, his skeletal structure is inscreased in size and strength, and his muscle growth greatly enchanced. He is implanted with a secondary hearth and superior lungs that enable him to survive wounds that would kill a normal human man thrice over. His blood is enhanced by organs that allow him to ingest poison without harm, filter his body of toxins and clot his wounds in an instant. Other organs allow his senses to be made preternaturally sharp or resist the effects if radiation... a Space Marine is implanted with the progenoid glands, organs that are repository of his genetic make-up"
So he`d win....you get the GW guys and Halo creators to team up and write a Astartes vs Spartans fight M.Chief will whooop some ass 
