well, if im not mistaken, one is kinetic and one is energy, so......whatever slot isn't taken up by your favorite Exotic. Or whichever isn't Masterworked. If both are MWed, Origin Story is better at making orbs since reloading resets the "multikill" counter (again, if im not mistaken about how that works), and Positive's Kill Clip perk doesn't gel as well as Origin's Rampage. And if you're asking in a PVP context, sorry, can't help ya, bud. No matter the game, I don't take PvP seriously, for the sake of my heart health.
Personally, I use Positive when I'm rocking Crimson. But for bigger fights with burn phases (like Calus), I'll use Coldheart and Ghost Primus.