Noble. Remember, they all are Spartans, even if Carter, Kat, Emile, Jun, and Six are all S-IIIs that are physically inferior to Jorge and Chief. I'll break it down: Carter is an adept tactician who could probably manufacture and adjust attack plans on the fly, and he's a pretty good shot with a DMR. Kat knows her way around a lot of electronics and depending on the battlefield, could use her surroundings to get an advantage. Jun is a great shot with a sniper rifle, and as long as he gets a good vantage point and doesn't open his big mouth, could take out Chief alone as long as the rest of Noble keeps him distracted and he isn't discovered. Emile is great in close quarters combat, but his skills are pretty limited beyond that. He'd probably serve best as a distraction. Jorge is a physically imposing S-II that can keep a chain gun on target and could at the very least hold his own against the Chief in a fistfight. He's probably the biggest threat to Chief. Noble Six is very skilled with all weapons and is no slouch with his fists either. Like Jorge, Chief would have to prioritize him. Overall, the only major threats to Chief in this fight are Jun, Jorge, and Noble Six. Carter is mainly dependent on having the entire squad in the fight, Kat is mainly dependent on the battlefield, and Emile is completely dependent on range. Noble has the advantage, but Chief would still have a fair chance against them. EDIT: Fun idea that I just had, tandem John with Kurt and watch Noble get wasted.