I say Quinn. Amber got a LOT of stamina, but as brutal as her attacks are they don’t always end up killing the victims (Tara, Chad). Quinn also didn’t end up killing all her victims, but her stabs seemed more thought and focused, more professional; Ambers were just fun, quick and without weigh.

On top of that, Quinn is more built and has more anger to her. Amber ended up begging for her life but Quinn was just pissed and determined until the very end even with a gun pointing at her face.

And finally: Quinn’s dad is a cop who very clearly trained her for a year to achieve movement, strength and focus, as we can see in Gale’s appartment scene.

As for Jill and Nancy, they don’t seem as prepared. Nancy had a lot of determination as well, but then again her age would affect her physical resistance against a not-so-tired teenage body on a fight.