SPARTANS (ancient greek, HALO, or mixed unit)
I guess it all comes down to equipment, if you're going that far... so lets say it's a pseudo-triathlon - run a marathon, swim a reasonably long distance, and then win a knife fight. You can bring your own knife (no more than 20cm blade, will be checked for poison), clothing not to exceed (or be less than... oh, god, my eyes...) reasonably sized shorts, and sandals.
Spartans(greek): bonus for being used to working at this tech level, penalty for being less "futurekind-evolutionized" than the far future types+-
Spartans(halo): penalty for not having their armor, penalty for not having their guns.--
Fremen: Bonus for being badass, bonus for being born knife fighters, penalty for water-freaking-out-ness-ness(isthataword?)++-
Dorsai: Bonus for being badass, bonus for being hyperspecialized soldiers ++
Mobile Infantry: Penalty for not having their jump-jetting minimechs with nuclear RPG launchers, bonus for being trained by that dude Zim to be badass anyway +-
so, halo loses because I tweaked the rules against them (Rules? What rules?) the MI and GreekSpartans wind up taking each other out in the semifinals, leaving the Fremen and Dorsai. Unfortunately, Stilgar slips on the wet ground near the water, giving juuuuuust enough of an opening for Graeme to win the day.
Damn. I should have made it something that didnt' involve swimming. Oh, well. Duncan Idaho will totally take him out in the rematch...