I'd say its a tie between Kratos and that guy from Shadow of the Colossus.
Kratos is rather obvious because of his skill with a large arsenal of weapons, which include: the Blades of Chaos, the Blade of Artemis, the Blade of Olympus, a magical Bow, Gorgon heads, lighting javelins (Zeus Lightning), a giant spear, a giant hammer, a pair of over-sized gauntlets, and I'm sure future posters will probably fill in any weapons that I missed.
The guy from Shadow of the Colossus ties with him not because of particular skill (he's mediocre with any weapon he picks up, be it sword or bow), but he ties with Kratos for his incredible stamina, resilience, and sheer dogged-determination to not give up on his girlfriend despite whatever that village shaman said.