MK 2, especially with the stuff like the insides coming out and what have you. Not to mention the body (or what's left of it) falling over when the move was done. I thought it was pretty stupid in MK 3/UMK 3/MK Trilogy that once you decapitate someone, they continued standing straight up, or the hands would hover next to the body if you knocked their torso in half or whatever. The bones and legs didn't look half as cool as the insides shown in MK 2 (why they didn't just use the character's own arms and legs for the Fatalities I don't know), not to mention in many cases you have two or three skulls, four pairs of legs/arms, an extra rip cage or two, etc. No to mention 90% of the moves ended up with your oponent exploding in some form or another. Got old after awhile.
MK 4 was better than MK 3 in most cases. It's only flaw was lack of original finishers. More than half the moves were just 3D versions of classic 2D Fatalities. It was cool seeing them in 3D, but at the same time seeing them in 3D doesn't make up for the lack of new Fatalities. The game also suffered from the 'explosion' factor as well. Too many sequences centered around the Fatality causing your oponent to explode. Once again it gets boring after a while.
MK 1 has great finishers, especially for its time. Overall, I'd rank MK 1 over MK 3 and 4 in terms of Fatalities. MK 3 and 4 may have had more, but MK 1 had quality. Most of MK 3's were either exploding moves or just plain stupid (such as Jax's Stomp, both of Kabal's, Liu Kang's Arcade drop, both of Rain/Human Smoke/Noob's, Kung Lao's Hat Slice, ect), let alone the multiple body parts. MK 4's, again nice looking, was pretty much the same-old, same-old and a lot of the orignal finishers weren't that great (exception being Quan Chi's leg rip). Most of the moves came straight out of MK 1-3 in some form or another. MK 1 at least had (at then) original and unique moves.
From best to worst, I'd go with 1) MK 2, 2) MK 1, 3) MK 4, and 4) MK 3.
