Shepard. Because he/she headbutts a krogan without hestitation if you choose to do so, even without a helmet. Headbutting another human is one thing, but headbutting a large alien whose skull is as thick and durable as that of an adult bull AND has a chitinous crest on the forehead? That's badass regardless of how you put it. He/she can stare down a krogan as well.
Kratos comes in as a close second though, because he's basically a demigod of manliness.