Roundhouse kicks. Of all the kicks in Martial Arts, I think the roundhouse kick has the most uses, the most different ways to throw it according to style, how you were taught or you taught yourself through trail and error, the most uses against resisting opponents, the most angles available to actual combat, the easiest to teach if you have patience and an understanding of movement, the more variants you can access to actually kick the ship out of someone in real combat, as a lead in, as a coup de grace, as a fake, as a distraction, as a part of a combination that will force an opponent to react, as a knock out shot, as a sweep, as a leg attack, as a jab, as a counter, as a statement, as a switch kick, as a power blast, damn, if you really know how to kick, it's as automatic as blinking.
I'm not sure if I've ever experienced two people....who don't know each other....that actually roundhouse kick the same way. In class maybe, not in actually mixing it up. Too many nuances, takes a few seconds to adjust sometimes. You might eat feet for a few seconds if you aren't careful.