Perhaps the Fatality in The Living Forest of MK9 because it's pretty boring.

Strykers head shot fatality
Kung Laos new fatalities

Also liked,Raiden's fatality from the SNES version of Mortal Kombat; if you don't know what he does,he uses his lightning powers to turn his opponent to a pile of ashes...look it up,it's pretty cool.I think it should be a download in the next game that will be on the XBOX 720 and PS4.Off Topic...Did you know that Midway spelled Raiden's name wrong in the SNES version of Mortal Kombat?,they spelled his name Rayden,not Raiden like it's supposed to be.

I will always love Havik's fatalities.

Sheeva's skin rip gives me the chills. Reptile's acid pukes always make my stomach churn. Noob Saibot's fatality with his shadow copy reminded me of the Noob-Smoke alliance.

But the best one is Kung Lao's fatality in Mortal Kombat: Shaoling Monks where he chops off the oppenent's arms, they run and he cuts their heads off. That one always makes me chuckle!

Now think about this: Reptile falling in the Dead Pool.

Kung Lao's Razor's Edge fatality in MK2011. That's the one that was shown at the end of the MK2011 reveal trailer, his 2nd fatality.

Sub-Zero's Spine Rip Fatality from Mortal Kombat 1. The legendary fatality that started it all & started Mortal Kombat to the legendary status it has now. It may not be as violent as most fatalities are today especially the new ones but to me its the best fatality of all time.

scorpions mk4 scorpion fatality is my all time favorite.

honorable mentions are

reptiles face feast from mk4.
cyrax internal grinder mkda fatality.
mk1 sub - zero's spine rip.

You can't have just 1 favorite Fatality. There's Kung Lao's Razor's Edge, Sub-Zero's Sine Rip, Fujin's Wind Crossbow, the list goes on.

Sub-Zeros MKD fatality

Leg freeze
Shatter legs
Let victim crawl away begging
face stomp
Sub-Zero wins. FATALITY.