In terms of how much I enjoy the characters (I just play for fun) looks (including gear options), joy of play and story characterisation:
1) Sindel. Gorgeous, sexy, huge breasts barely contained, she's clearly loving being an evil man-eater, she’s brought the sexy back to MK, her banshee scream sounds amazing and am totally fine with her retcon (plus I can restyle her hair and choose her FMBs! And yes I love that shit haha!).
A lot of love went into making this ass:
2) Shang. Can’t go wrong with Cary back for the third time, especially with the movie skin. Only downsides... don’t care for either fatality and no announcer pack!
3) Shao Kahn. Bit of a hoss with no depth to his character, would prefer a more evil intelligently scheming Kahn akin to how he was portrayed in Conquest, but he’s still an enjoyable behemoth and looks great.
4) Nightwolf. He’s a bit dull as a character, he makes the Defenders of the Realm loser look positively charismatic by comparison, would have preferred him white eyed and more savage, and the cycling helmets are ridiculous, but looks an absolute beast in revenant mode and should have been his default look (I pretend it's just war paint anyway).
Then the guests in this order (because I'll always rank original characters higher than guests):
5) Spawn, since he can almost masquerade as a real MK character and enjoy some of his interactions (also helps I have very little experience with that franchise, so he doesn't stick out as much for me as being from another IP)
And last the two I consider basically novelty characters.
6) Terminator (he was at least once the cold unfeeling hunter in basically a slasher horror)... although I think he plays like shit
7) Joker