It doesn't matter. Competitive battling is completely separate from the main game, and virtually unchanged between X/Y and ORAS.
Most important thing to learn is types and abilities, once you learn weaknesses and strengths then you can start building teams. It's all about team synergy.
Here's a perfect example of 2 Pokemon with amazing synergy,
Ferrothorn and
Chandelure. You can see below that Ferrothorn is 4x weak to fire type attacks (because grass is 2x weak, and steel is 2x weak),
However, Chandelure has an ability called "
Flash Fire".
So when Ferrothorn is in against a fire type and you have Chandelure, the mind games begin. Do they choose a fire type move and risk you switching in Chandelure and getting a boost? :lenny: