I'm really in love with every cyborg ninja's x-ray.
3rd: Cyrax: The anti air always catches you off guard. The blue streaks look pretty as he disassembles to teleport proximal to you in the air. Then that piledriver is brutal. I mean not only does he crack your skull and neck with the sheer force of the 10-foot fall, but he puts his foot on top of your skull for good measure. Can you imagine how much Cyrax weighs coated in all that durable metal, with a giant blade and a seemingly infinite supply of bombs in his chest? All that weight, focused on one leg, focused on your skull. Done.
2nd: Cyb Zero: He dive kicks past your face. As your brain is processing how much you just soiled yourself, he cracks your skull with an oversized iceball that he assembled in his hand. If that isn't enough, he assembles an even more oversized ice sword and, even though it has a fairly blunt point, it doesn't stop him from stabbing that thick f**ker through every major organ you thought you had. The sword doesn't just disappear though, he uses it as a handle to flip you onto the floor, letting ice shards shatter inside of you. Internal bleeding much?
1st: Sektor: Hands down my favorite. A rocket to the face is usually enough to make anyone have a bad day. But then as you're looking down thinking FML, there's a metal fist approaching your face. I'm not even going to talk about the spine burning/breaking.