Every single character in MK9 worth to be learned .... the reasons ? simple :
- some, of course, being your favourite, have priority, so, you learn to kick ass with, for competitive purpose
- others, you learn to know the bad matchups your main characters have, so, you learn about your possible nemesis in this game, and how to counter attack, and defend against
- and finally, when you get tired, bored, and fed up of playing the same characters, over and over again, you learn the rest of the roster, for fun, when you want to learn new stuff from new character, and play with friends or ladder, for stress relief time reason
You should learn the minimal basics of every character.