Rick is too unstable; Morgan too unwilling to kill; Gabriel too, no, just no to Gabriel. It’s a two-woman race for second place: the katana-wielding Michonne, or unassuming Carol. I’d choose the latter for that very reason. She fooled the gullible idiots at Alexandria into thinking she’s a humble, cookie-baking house wife, when really she’s an unstoppable murder machine.
Take a look at her kill count, courtesy of Visu.
For the first 35 episodes of The Walking Dead, eight kills; the next 16 episodes, 14 kills. Carol went even more commando in season five, when she notched 21 fatalities, through stabbings, explosions, and shootings. And that’s how you go from “outcast to unkillable badass.”