I want to say Johnny, because Johnny is my first main since I played MK for the first time and he'll always be my favorite MK character. But right now, in the current build he's way too frustrating because of his whiffing issues. There's like 6-7 characters where you can have fun and really enjoying the character. When I pick Johnny and the opponent picks his character, I spend the whole loading time trying to remember what's working against this character.
Right now I'm having a lot of fun with Kollector, he is a solid character but could use a buff or two.
So my vote goes to Kollector