Whenever I first dive into a game, I always pick the most straightforward character and play as him/her in order to get a grasp of the game's mechanics and how the combo system works.
Take Street Fighter, for example. Shotos are pretty much (albeit not always) the most fundamental characters to play. Ryu, equipped with a spacing tool (Fireball/Hadouken), an anti air special(Shoryuken), and a potentially damaging combo ender (Tatsumaki), best fits this straightforwardness.
In Mortal Kombat 9, I chose Liu Kang for pretty much the same reason. His combos are straightforward and damaging (the fact that he can combo into and from his X-Ray helps a lot), he has a really good spacing tool (instant air fireballs), and really good mixup strings and 50/50s in order to keep the pressure on the opponent.