More love for Kung Lao's hat slice. I remember my reaction to seeing it for the first time; Kung Lao did the slice, the opponent fell to their knees appearing otherwise unharmed, only to notice a thin red vertical line starting to form before... RIP. Going from "what the hell happened, he looks fine" to "holy shit, that's awesome".
Anyway, as far as MK1, I'd probably place Sub-Zero's spine rip as number one, followed by Raiden's head explosion (the amount of blood was extremely impressive) and Kano's heart rip.