Season 15: I admittedly want to say Salina, given she's beaten four queens overall and sent home three (Amethyst, bested Luxx, and sent home Spice and Malaysia) if you want to be super "technical", but Jax, Anetra, and Sasha are also sickening AF, so I feel it's a matter of preference.

Season 16: Definitely Morphine considering she has the most wins or "heads on the mantles", however you'd say it (Xunami, Mhi'ya, Dawn, Geneva, Mirage, and Megami). 

Season 17: I'm genuinely divided between Lana (beating/eliminating Hormona, Crystal, Lydia, with her loss to Sam being her best lipsync, then later Crystal again, totaling 4 wins), Kori (beating/eliminating Joella, Acacia, Arrietty, and both Lana and Lydia simultaneously, totaling 4 wins vs 5 queens?), and Suzie (having beaten Jewels, Joella, Lucky, and Kori, totaling 4 wins). 

I *kinda* want to say Kori given she's sent home/beaten the most queens, but Suzie also won the Lipsync Smackdown, so I'll ultimately say Suzie just by a midge even though both are even for me (with Morphine branding Suzie as the only one who could beat her). I guess it depends on how you perceive the concept of a Lipsync Assassin (also don't jump if I missed a lipsync/miscalculated a stat, math is not my friend).

Bonus question: form a team of three queens. The remainder will try to kill you or whatever, I don't know (for me Sasha Colby, Morphine, and Suzie).

With US Season 18 announced, who was THE Lipsync Assassin of the past three main seasons?