Considering that the alien has acidic blood, superhuman strength and agility, not to mention a tongue that can extend a fair length from its face, ending in a vicious maw, I'd say that the Alien wins.
That, and the "ninja" looks more like a space prostitute who just so happens to be carrying a sword.
That, and the "ninja" looks more like a space prostitute who just so happens to be carrying a sword.