Kabal's is my current favorite because it utilizes his two fighting aspects in the most unique way + having your shins broken feels like it could be the most painful thing to happen to you.
But other notables go to: Kitana, Baraka (two of the most over-the-top brutals), Stryker and Quan Chi (for incorporating their personalities so well) and Reptile for how visually striking it is. Sonya's is also extremely cool because we get to see her bicycle kick and i love the little combo that leads up to it.
In all honesty, all the X-Rays look fantastic and there's not one that i feel is 'bad'.