I liked all of them so far, but Leatherface and Triborg have the best ones.
Alien I was a little disappointed with, owing to the lack of any Facehugger finishers (I'm *hoping* there's a facehugger rape Brutality) Otherwise, I liked them! I'm a sucker for all things bisection (#1 ryona type for me) and Alien's tail stab/ torso rip is just great in that regards. Nice build-up, slow and painful, really sexy spinning body parts in the slow-mo; only thing I'd change is her lower half landing ass-up instead of down.
Alien's second fatality has a WONDERFUL build-up; I love the stabbing and the way Alien pulls its victim in close, staring her right in the eyes. That's the sort of thing they should have really given to Baraka! The actual kill is a let-down; I was hoping for a more violent vore ending, and honestly if Alien had scarfed it's victim this might well have been my favorite of the new finishers. As it is, it's really good in terms of the entire game, but only average in the context of this new release.
Bo Rai Cho's explosive fatality is awesome. Again, a very nice, perilous leadup to the main event. It incorporates two things I like: dousing a helpless heroine in flammable liquid, and bisections (explosive, in this case). The flaming lower body is a nice touch!
The second fatality is less awesome. It's gory and painful-looking, but it doesn't make much sense to me. Why is the booze making her puke out her intestines? Is it poison booze? They should have gone for another fart fatality, but oh well.
Triborg's gang rape fatality is really cool, especially that last bit, where Sektor splits her in half and they hold her up like a fucking trophy. The "trophy display" trope was used to great effect in previous MK games - SubZero, Kung Lao, and Noob all had similar victory poses in MK9, for example. This trope is not used as much in MKX, which is a disappointment.
The peril machine fatality is even better. I've actually had dreams about things like that happening to Kitana, so this fatality is going right up near the top of my list! That last shot - when the beautiful girl has been reduced to a processed block of meat - is cruel and cold and ever so sexy.
Leatherface's split fatality is OK. I love the way his victim screams and falls to her knees, but it's a little too close to some of the other fatalities for my liking (e.g. the scythe faction kill, or Kung Lao's flower fatality).
His meat hook fatality, on the other hand, is AMAZING. Possibly the best fatality in MKX, and I do not say that lightly. Again, bisections are amazing, and you've got the whole bondage/peril aspect while the defeated heroine is dangling on Leatherface's meat hook.. It reminds me of my favorite fatality from War Gods, and - like the machine processing above - is another scenarios I've envisioned in the past. Pretty much perfect. 10/10, now if only if was on the PC, and we could use the camera hack...!!!