There's one of these posts every month it seems. It depends entirely on how the universe's tech transfers. Guardians have programmable matter woven into all of their tech, space magic, and insanely tech'd out suits similar to Chief. Their weapons are things the UNSC would go mad considering as even possible. A Guardian's abilities are unlimited in quantity, but have a cooldown. They also have their Supers but I'm not counting them. Chief has MUCH more basic weapons, but he's Capt America on Steroids and Lucky Charms™. He also doesn't have to wait on cooldowns to use his 'nades, but they're finite. It's even unknown as to how different the rounds fired from UNSC weapons differ to that of Destiny's. So many "What ifs" and unknowns to accurately make a statement, but in a 1v1 fisticuffs without Light involved (the thing that makes a Guardian a Guardian) Chief would win.