I've killed a lot of sims for the Black Widow Challenge and I've gotta say my favorite way to kill sims is either drowning or hysteria. I've tried starving but it takes soooo long omg. But what meth...
Pufferfish Ngiri is the most fun way for me. If it's badly cooked and a sim is in a bad mood.. well lets just say they'll be getting a visit from a dark and shrouded figure.