Auron was pretty bad-ass, but I have to agree with the people saying Darth Revan. This guy somehow decides the fates of entire galaxies simply by choosing which side he's going to be on. Combine that with Bastila, who can turn battles with her mind and is therefore arguably an even bigger badass, and you have team badass on a galactic scale. That said, Bastila can get a bit emotional sometimes, so she doesn't quite have that stoic badass mindset.
Link's also pretty damn tough. Many heroes can boast about saving the world. How many heroes can boast about saving a world (Termina) at the age of ten?... and again previously without the slightest bit of training? (Ocarina of time) That said Link does seem to possess improbable fencing skills... that and he's never fought someone who actually knows how to use a sword (he just swings wildly, though he is astonishingly quick with a blade and to dodge... the fact that he's insanely talented just adds to the badass.)
Come to think of it, does Hyrule have anyone who knows how to use a sword? The gerudo's seem to know a thing or two, Link just surrenders when engaged by them, unless they're also using swords. (He kills 4 sword-wielders when rescuing captives.)
Link and Revan also both possess that stoic mindset required of most badass characters. They may feel emotions, but unless its a big surprise or something really REALLY scary (Ganondorf himself bearing down on him from a horse while Link is still in his child form) Link doesn't bat an eyelid, and Revan (depending on the dialogue choices you take) may not show any emotions at all! That said, I'm sure Link's cried as a child on a few occasions, the fairy who joins him on his trip to Termina tells him not to cry when he's first transformed into a deku, but considering the circumstances I think even the most stoic of characters could be excused for breaking down.
Ratchet also seems to save galaxies on a daily basis, going from a humble mechanic to a hardened soldier capable of beating up armies of robots armed with nothing but a makeshift hatchet in some circumstances (omniwrench) He's seriously tough.
