Speaking of raw power, hands down the Spartans/Chief would win. He could easily destroy a guardian. With abilities in mind (space magic in destiny/ spartan abilities in halo) it would be a close fight but i still think spartans would win. They may not have fiery hammers of hell or golden penis guns that kill you instantly (except for CE magnum), but spartans know how to handle impossible missions and get positive outcomes. The chief took down scarabs, wraiths, covenant ships single handedly and even survived falling from space onto the surface of earth. Guardians are not battle geniuses but they do know how to persevere and use what they can from the remains of the Golden Age and they're abilities are pretty damn cool. The similarities of their abilities : ground slam=fist of havoc; bubble shield=ward of light but the guardians still have the nova bomb, blade dancer, radiance, stormcaller, and shadow shot to their advantage. Even so i still believe that the Chief would. He was able to survive his encounter with the gravemind, the flood, the Ur-Didact and the Composer as well as the multi bodied Warden and the Guardians(from Halo 5). They all had some sort of special ability beyond that of physical prowess/strength and yet he still defeated most of them/ survived them. The Guardians had to team up together and use relics to even damage Atheon, Crota, and Oryx. It would be a really close fight but overall i do believe Chief would win against a guardian.