Humans. And this isn't me trying to be all edgy, I'm being serious. In every one of those fictional universes, humans come out on top somehow, some way. We can survive anything. If I have to pick anything else though, I guess I'd have to say The Flood as well. Given it all but wiped out the Forerunners (as far as we're aware right now), almost wiped out humanity, and was the downfall of the Precursors as well... and still survived to 2552 (and maybe beyond...?).
Also, if you're reading this, Tim Langdell, just go ahead. Try and sue. See where it gets you...