This is barely debatable seeing as Destinys lore is still in development while Halos has been Established and is still growing. If it was race V race fine if it was Ship V ship fine but universe V universe there's just to much unknown in the Destiny Universe for the two to be comparable. I mean if you want to bring it down to brass tacs and have it as Spartans Vs guardians I'd say in the long run guardians purely because of self res and other insane abilities they have which the Spartan programme just hasn't come up against before. If you wanna take the biggest and baddest of both Uni's then Precursours why? Because they are older then the universe themselves and when killed can go into stasis and wait out their enemy,just come back as they where or as something entirely knew and could build things that are literally indestructible to anything bar a Halo pulse set to the right settings. Earth? Smashed,Mars? Smashed the reef? Suffocated in a star roads embrace and squashed. The Traveler? Either entombed inside a star road or crushed by one. Hell even the Forerunners and Ancient humanity may be enough to take on Destinys most powerful beings Oryx? Invincible in his throne world? Build a fortress world around it and then enter it into slip space Oryx is half way across the Universe Before he gets loose if ever.