Ivy from Soul Calibur. And no, not for the reason you're thinking. Just to be sure, we'll say Soul Calibur 3 Ivy, before they doubled the size of her ta-tas for no good reason the f***s. Anyway, the reason why is that she's british, a genius, she's heartless but not necessarily evil (like me), and she's what we call in the biz a "bad ass".
No, wait. I take it back. I choose Aya Brea from the Parasite Eve series. Eternally youthful, intelligent, psychically gifted (best way to describe it, look the game up), but still has a softer side. Also, she holds the honour of being maybe the only blonde in the world I'd ever consider dating. I can't stand the colour yellow.