Omastar for me too. It's just something about its entire appearance that makes it so cool.
Kabutops might be cool with the schytes and all, until you start thinking about how it would work in action. The blades aren't very practically hinged for slashing, and look far too heavy to be used effectively with those tiny arms. It also needs an enormous free radius to swing the blade-like arms.
Omastar, on the other hand... it's slow, especially on land. It is only threatening from the front. However, I can imagine it pivoting quickly around to always face the enemy. And dish out pain. Lots of pain. That mouth is like the endpiece of some powerful cannon, always ready to spring open and unleash a tremendous jet of water. Its spikes are like rockets, mounted ready to fire, regrow instantly, and fire again. The eyes... they see you. And the arms dance and wiggle while it battles. What's not to like about Omastar?